The Taliban nominate a U.N. envoy, complicating a quandary for the General Assembly.

The Taliban have nominated an ambassador to represent Afghanistan at the United Nations, U.N. officials said Tuesday, injecting a new twist into what was already a delicate diplomatic quandary in the global organization.

The nomination, submitted to Secretary General António Guterres on Monday, sets up a showdown with the envoy of Afghanistan’s toppled government, Ghulam Isaczai, who has so far retained his post.

The showdown may not be resolved soon. But it raised the startling prospect that the Taliban — the violent, extremist Islamic movement that retook power last month as the American-backed government collapsed — would occupy an ambassador’s seat at the United Nations.

Stéphane Dujarric, a spokesman for Mr. Guterres, confirmed a Reuters report that the secretary general had been notified of the Taliban request in a letter signed by Amir Khan Muttaqi, identified as the movement’s foreign minister. The letter stated that the Taliban’s choice of U.N. ambassador was Suhail Shaheen, the movement’s spokesman based in Doha, Qatar.

The letter further stated that Mr. Muttaqi wanted to speak at the General Assembly, which got underway on Tuesday and ends next Monday. On Wednesday, Bilal Karimi, an aide to the Taliban’s chief spokesman, Zabiullah Mujahid, confirmed that the Taliban had sent the letter.

Mr. Dujarric said the Taliban’s request had been forwarded to the General Assembly’s Credentials Committee, a nine-member group that includes the United States. It remained unclear on Tuesday when the committee might evaluate the request.

Pakistan’s foreign minister, Shah Mahmood Qureshi, who knew about the Taliban’s request, said it raised a number of questions about Mr. Shaheen and those in the Taliban hierarchy who had picked him.

“Who is he representing?” Mr. Qureshi said, responding to questions about the request during a session with reporters on Afghanistan’s future, held by the Foreign Press Association on the sidelines of the General Assembly. “Who is he reporting to? What kind of communication can you have with a person at the U.N. who is not recognized? It is a complex and evolving situation.”

The Taliban’s triumphal return to control in Afghanistan is among the crises confronting the General Assembly this week, along with Myanmar’s brutal military coup early this year. Both events created a conundrum for the world’s biggest diplomatic gathering: Who is the rightful representative of each country?

The Taliban remain subject to U.N. economic sanctions. Many countries, including the United States, have said that any Taliban request to replace Afghanistan’s envoy at the 193-member organization would need to undergo careful review.

In Myanmar, the junta that seized power in February and has been widely condemned for a deadly crackdown on opponents also has sought to replace the U.N. ambassador of the deposed government with a junta loyalist.

Envoys from all kinds of political systems, including parliamentary democracies, monarchies and dictatorships, have long worked at the United Nations, the one place in the world where even governments that reject one another’s ideologies enjoy some measure of equal standing. Still, there are standards to verify the legitimacy of both the envoys and the governments they represent.

“Normally a country has the right to nominate somebody,” Volkan Bozkir, a Turkish statesman and the departing president of the General Assembly, told reporters at his farewell news conference this month.

“We can’t say, ‘I don’t like this government,’” Mr. Bozkir said, when seeking to resolve United Nations disputes over who is — and is not — a country’s rightful envoy.

A seat at the United Nations carries symbolic significance, a benchmark of a government’s credibility and acceptance in the world community even if rivals oppose it.

United Nations membership affords governments an opportunity not only to speak and be heard in the General Assembly, but also to participate in a range of other U.N. agencies like the World Health Organization and Human Rights Council. So the credentialing of a country’s ambassador to speak on its behalf is enormously important.