Ambassador Kyaw Moe Tun spectacularly broke with the junta before the General Assembly on Friday in an emotional plea for help to restore ousted civilian leader Aung San Suu Kyi.

The next day, the junta said the envoy had been sacked, but on Monday, Kyaw Moe Tun sent a letter to the president of the UN General Assembly to say that he still holds the post.

"The perpetrators of the unlawful coup... have no authority to countermand the legitimate authority of the president of my country," said the letter obtained by AFP, referring to Suu Kyi.

"I wish therefore to confirm to you that I remain Myanmar's permanent representative to the United Nations," he added.

On Tuesday, Myanmar's foreign ministry sent a note verbale to the UN, also obtained by AFP, claiming Kyaw Moe Tun had been removed.

"The ministry of foreign affairs... has the honour to inform that the state administration council of the republic of the Union of Myanmar terminated the duties and responsibilities of ambassador Kyaw Moe Tun," the note said.

"At present, Tin Maung Naing, deputy permanent representative ambassador, has been assigned as the charge d'affaires ad interim of the permanent mission," the note added.

UN spokesman Stephane Dujarric told a press briefing that the body had received the two "contradictory" letters.

"We are taking a look at those letters, where they came from and what we will do," he said.

The United States backed Kyaw Moe Tun and hailed his "bravery," with a State Department spokesman saying "we understand that the permanent representative remains in his position."

"We will continue to oppose the military coup and we will continue to support the restoration of Burma's democratically elected civilian government," the US spokesman said.

US envoy to the UN Linda Thomas-Greenfield also met virtually with Kyaw Moe Tun on Tuesday to express her support.

UN accreditation and protocol committees will look into the issue and then refer it to the General Assembly.

Dujarric said that the UN envoy to Myanmar, Christine Schraner Burgener, who is currently in Switzerland, "continues her conversations with various parties regarding the current situation."

On Friday, Burgener said that "it is important the international community does not lend legitimacy or recognition to this regime," and called for the international community to press for a return to democracy.