BANGKOK — A United States Justice Department complaint filed in federal court this week directly contradicts repeated assertions by the Malaysian prime minister, Najib Razak, about the origins and purpose of hundreds of millions of dollars that ended up in his personal bank accounts.
While Mr. Najib and other Malaysian officials have insisted that the money was a gift from an unidentified Saudi donor, the Justice Department said that it was stolen from a Malaysian government investment fund that Mr. Najib oversaw. Mr. Najib has said he never received any money from the fund.
The court filing, one of several complaints filed Wednesday in a federal money-laundering investigation, provides the first official public documentation of transactions that challenge Mr. Najib’s version of events in a scandal that has battered his government for the past year.
The revelations could undermine his credibility and give new ammunition to a movement to force him from office. However, he maintains firm control over his governing party and has successfully stifled opposition with the firing of critics from party posts, the closing of online news outlets and the criminal prosecution of social media detractors and political opponents.
Mr. Najib, who has acknowledged receiving the money but said he broke no laws and took nothing for personal gain, told reporters on Thursday that his government would “fully cooperate” with the Justice Department action.
“Allow the process to take its course,” he said, “but I want to say categorically that we are serious about good governance.”
A spokesman for Mr. Najib, reached late Thursday, said that the prime minister had not changed his position that the money he received was a gift from a Saudi donor and that he gave most of it back because he did not need it.