Two Myanmar citizens have been arrested in New York state for plotting with an arms dealer in Thailand - who sells weapons to the Burmese military - to kill or injure Myanmar's ambassador to the United Nations, US authorities said on Friday.

Ambassador Kyaw Moe Tun, who represents Myanmar's elected civilian government which was overthrown by the military in February, told Reuters on Wednesday that a threat had been made against him and U.S. authorities had stepped up his security.

The US Attorney's Office for the Southern District of New York said on Friday that Phyo Hein Htut, 28, and Ye Hein Zaw, 20, had each been charged with one count of conspiracy to assault and make a violent attack upon a foreign official, which carries a maximum sentence of five years in prison.

The ambassador did not immediately respond to a request for comment on the charges. Myanmar's junta fired him in February, but for now he remains the country's UN envoy because the United Nations has not acknowledged the junta.

According to the legal complaint, Phyo Hein Htut told FBI investigators that the arms dealer in Thailand had contacted him online and offered him money to hire attackers to hurt the ambassador and force him to step down.

If the ambassador did not step down, then the arms dealer proposed that the attackers would kill him, according to the complaint. Phyo Hein Htut and the arms dealer then agreed on a plan to tamper with the ambassador's car to cause a crash.

Ye Hein Zaw contacted Phyo Hein Htut and made two money transfers totaling $4,000 in late July, according to the complaint. Phyo Hein Htut told the FBI he was supposed to receive an additional $1,000 after the attack was completed.

A volunteer security guard at Myanmar's UN mission told the FBI on Tuesday that Phyo Hein Htut had told him about the plan "to hire a hitman to kill or injure the ambassador."

The complaint said Ye Hein Zaw admitted he transferred the money to Phyo Hein Htut, that he regularly sends money to others on behalf of the arms dealer and recently booked travel to the United States for two other people at the arms dealer's request.

"These defendants reached across borders and oceans in designing a violent plot against an international leader on United States soil," New York Police Department Commissioner Dermot Shea said in a statement.