1139 GMT: The dead brother is identified as 19-year-old Djohar Tsarnaev.
A Russian-language page on the VKontakte social media website, Russia's equivalent to Facebook, lists a 19-year-old named Djohar Tsarnaev. The site says that he graduated Cambridge Ringe & Latin School 2011, identifies "Islam" as his world view, and "career and money" as his main goals in life.
It also lists information about Chechnya and Islam as well as different mosques around the world, and retells some jokes about the unfair mistreatment of Muslims in Chechnya.
1124 GMT: Sunrise in Watertown shows streets empty to call but law enforcement. Armored vehicles are the only vehicles rolling down the streets.
1118 GMT: All schools in Boston close for the day. Even "essential employees," who would normally report to work even in the event of an emergency, in the Allston Brighton neighborhood, are told to stay in their homes.
Residents are told not to even open their doors to anyone but police with identification.
1106 GMT: The entire area around Watertown is shut down by police. Traffic is stopped and businesses have been told to stay closed. Media is announcing police plans to conduct "controlled explosions" in the neighorhoods.
1102 GMT: US media reports the men have lived in the United States for at least a year.
1058 GMT: NBC News is reporting the two suspects are brothers of Chechen desent.
1048 GMT: Eyewitnesses are starting to describe the dramatic early-morning stand-off.
Peter Jennings, 33, told the Boston Globe he was awoken by a loud explosion at just before 1:00 am (local time).
?It sounded like a stick of dynamite went off,? he told the newspaper.
Jennings told the newspaper the air smelled like ?at the end of a fireworks show, like a wick smell.?
1036 GMT: Some more details are starting to trickle though about the car-chase, as police say the two suspects hijacked a Mercedes car in Cambridge, Massachusetts, before eventually freeing the terrified driver in Watertown.
Boston police say the first suspect had explosives on his body, and there were fears the second suspect still at large was also strapped with bombs.
1024 GMT: Some of the world's leading universities have been forced to cancel classes amid the ongoing security lockdown near Boston.
Harvard University and MIT cancel classes, citing security concerns.
1013 GMT: A brief recap on the main points in this dramatic manhunt: -
-- Armed police have launched a massive manhunt in Watertown for a gunman who they say is one of the two suspects in Monday's Boston Marathon bombing.
-- Police in Massachusetts, confirm that the second suspect in the Boston Marathon bombing has been killed after a dramatic car-chase and shootout in the sleepy town, which lies some 10 kilometres from Boston
-- Massachusetts authorities urge all Watertown residents to stay indoors and suspend all public transport into Boston, as they tighten the noose in the ongoing search for the 'white-cap' suspect who they describe as "armed and dangerous".
1002 GMT: More details are coming through on the widening manhunt for the 'white cap' suspect.
Boston officials are urging people in western Boston and at least six neighboring towns to stay indoors as Massachusetts governor Deval Patrick authorises the suspension of all buses and trains into Boston.
0951 GMT: Watertown is effectively under curfew as police continue their manhunt and refuse to allow traffic to enter or leave the town.
0950 GMT: POLICE ASK ALL WATERTOWN BUSINESSES TO STAY CLOSED, AND URGES ALL RESIDENTS TO STAY INDOORS
0948 GMT: BOSTON POLICE SUSPEND ALL SYSTEM TRANSPORT
0941 GMT: Officials at the Boston hospital decline to comment if the suspect died from injuries consistent with a suicide bomb.
They confirm that he had "shrapnel and thermal injuries to his trunk" but refuse to speculate on what might have caused the injuries.
0940 GMT: The suspect who was fatally wounded in the shootout, arrived at the Beth Israel Medical Center at 01.10am (local time), doctors say.
He was undergoing CPR as a result of "traumatic arrest" from his injuries, and was pronounced dead at 01.35am (local time)
0930 GMT: The suspect was brought under police guard to the Beth Israel Medical Centre.
Dr Richard Wolfe tells reporters that he died of multiple injuries despite efforts to resuscitate him.
0928 GMT: In an emotional press conference, one of the doctors who treated the terror suspect who was critically wounded in the shootout, describes how he was forced "to set his emotions aside, and do his best regardless of who they are or the circumstances"
0927 GMT: Doctors at a Boston hospital say the 'black-hat suspect' who was killed in the Watertown shootout had "blast and gunshot wounds"
0918 GMT: The dramatic manhunt and car chase took place at 10pm (Boston time) and just in case anyone slept through the shooting and explosions, police are sending robo-calls to every household, ensuring they stay indoors until the suspect is apprehended.
0916 GMT: Hundreds of police carrying shotguns and assault rifles are scouring the streets of Watertown, which lies about 10 kilometres from Boston.
0914 GMT: Boston police say the suspects first tried to rob a convenience store in Cambridge, across the river from Boston, before they carjacked a vehicle before the shootout.
0906 GMT: Police have released some more details of the shootout, and describe how one of the suspects was hit and died later in hospital.
A police officer was shot dead in the shootout while another officer was wounded, Davis said.
0850 GMT: A frightening and nerve-wracking wait for Watertown residents as heavily-armed police set up a 20-block perimeter around the Vasser and Main districts of Watertown as they hunt for the armed suspect.
0846 GMT:Some more information on the 'white hat suspect' who is still at large, who police describe as a light-skinned, Caucasian.
0826 GMT: Boston police say the suspects were terrorists, who 'came here to to kill people'.
0825GMT: Police are advising residents to stay indoors and not let anyone into their home as they conduct house-to-house search for the 'white hat suspect' who they describe as "armed and dangerous".
0823GMT: The Boston Police Commissioner describes the dramatic hunt for the suspects, saying the 'terrorists' threw explosive devices from their SUV during a high-speed car chase through the sleepy town.
0822 GMT: Speaking to The Boston Globe residents described the neighborhood where the police operation is ongoing as usually safe and family oriented.
One newly moved in woman, pointed across an improvised police barrier to a shop where she told the Globe: "I was buying ice cream right there just this afternoon.?
0812 GMT: Edward Davies Boston Police Commissioner has tweeted: "One suspect dead, one at large, white hat suspect at large."
The white hat suspect refers to the FBI's Suspect Two from their photos.
0803 GMT: Local TV channels are reporting that a Boston marathon bombing suspect captured by police has died in hospital.
0756 GMT: John Atwater, a TV reporter for WCVB, has just tweeted:
"Officer says they are about to detonate a device in the area of Dexter and Laurel. Air horn will precede explosion.
"Officers tonight have said 'explosives are everywhere'?
0754 GMT: Mass State Police have tweeted: "Police will be going door by door, street by street, in and around Watertown. Police will be clearly identified. It is a fluid situation.
"If any concerns about someone at door, call 911 immediately. Repeat--Do not answer door, stay away from windows, keep doors locked."
0748 GMT: Massachusetts State Police have tweeted: "Residents in and around Watertown should stay in their residences. Do NOT answer door unless it is an identified police officer."
0745 GMT: Police SWAT teams have sealed off the town, reports say, and television reports show police teams moving through the streets block by block.
0740 GMT: Reports say the operation began after a robbery at a gas station was followed by the killing of the police officer on the campus of MIT and a car chase to Watertown.
One suspect was caught in Watertown, which is near Boston, while police are still hunting for the second man.
A second police officer was wounded during a gunfight in Watertown, reports say.
0733 GMT: One resident told NBC News about a police standoff outside his house.
Andrew Kitzenberg said earlier two shooters and police had engaged in gunfire for several minutes. The gunmen used "bombs that looked like grenades," Kitzenberg told NBC News.
0727 GMT: Earlier in the video released by the FBI the two men are seen walking calmly, one a few paces behind the other, weaving between crowds on Boston's Boylston Street where the race finished.
Both appeared to be young men, one dressed in a white baseball cap and the other in a black cap. But the FBI gave no details of their identities or origin, naming them only as Suspect One and Suspect Two.
Rick DesLauriers, Federal Bureau of Investigation (FBI) chief in Boston said other images indicated the man in the white cap placed a bomb outside a restaurant in the street in the minutes before the blasts tore through the crowds.
0725 GMT: A tweet from a reporter on the ground, Michael Skolnik says police told him: "White suspect with grey hoodie should be considered armed and extremely dangerous. Possibly with an assault rifle and explosives."
0720 GMT: The Boston Globe is reporting that police officers and dog units have swept the MIT campus.
Students at the university were earlier told to remain inside while police, including SWAT teams combed the campus block by block, searching buildings, bushes and alleys.
0717 GMT: An FBI agent has told the media that the situation remains extremely dangerous. The Cambridge bomb squad arrived in Watertown shortly after 1:30 a.m. local time.
0715 GMT: The whole drama started some two hours earlier when a gunman shot dead an MIT campus policeman sparking a massive police operation.
This was shortly followed by reports of gunfire and explosions.
MIT is in Cambridge, Massachusetts, just across the Charles River from Boston, where three people were killed and 180 injured in a double bomb attack on the city's marathon on Monday.
Earlier on Thursday the FBI had released pictures and video of two men suspected of planting the Boston marathon bombs, appealing for help to identify the pair who were carrying large backpacks.
Two bombs were placed around the marathon finish line on Monday, spraying nails, ball bearings and other metal fragments into the crowds, many of whom suffered horrific injuries.
0712 GMT: The suspect was caught in Watertown near the US city of Boston after a chase which started with the killing of a police officer at the elite Massachusetts Institute of Technology, the newspaper reports.
0710 GMT: The Boston Globe is reporting that police have captured one of the Boston marathon bombing suspects but are still chasing a second suspect.
WELCOME TO AFP'S LIVE REPORT on the police operation in streets close to the prestigious Massachusetts Institute of Technology where gunfire and explosions erupted after a police officer was shot dead.Local media said one person may have been shot in the incidents as heavily armed police launched a major manhunt following the killing on the MIT campus near the US city of Boston.