Thailand's army declares martial law in broadcast on military TV
Thailand's army has declared martial law in an announcement on military TV.
The announcement said martial law had been invoked "to restore peace and order for people from all sides", stressing that the move "was not a coup".
"The public do not need to panic but can still live their lives as normal," it added.
Months of anti-government protests in Thailand have left 28 people dead and hundreds wounded, and the country's political crisis intensified earlier this month when prime minister Yingluck Shinawatra was thrown out of office.
The ABC's South East Asia correspondent Samantha Hawley says the Thai military is moving to take control of key areas of the capital Bangkok.
Thailand's powerful military has launched or attempted 18 coups in 81 years of fragile democracy, but in recent years it had sought to ease fears that yet another coup was imminent.
But last weekend army chief General Prayuth Chan-ocha warned his forces were ready to use force to deal with any future violence
"I want to warn every group, especially those using violence and war weapons against innocent civilians, to stop now," he said.
"If this goes on the military may be needed to come out and restore peace and order."
Last week Thailand's Election Commission called for national polls planned for July to be postponed because of the political unrest escalating in the kingdom.
The appeal came after three anti-government protesters were killed and 23 wounded in a gun and grenade attack on their protest site in Bangkok.
Former prime minister Ms Yingluck was ousted by a Thai court for abuse of power earlier this month after six months of protests against her government.
A caretaker government was installed but that did little to curb the protests.
Thailand has been riven by political divisions since 2006, when Ms Yingluck's older brother Thaksin Shinawatra was ousted in a military coup after frictions with the country's royalist establishment.
Thaksin-led or aligned parties have won every election since 2001, but four prime ministers have been removed by coups or court rulings.