Last week, the Taliban wrote a letter to UN Secretary-General requesting that its new foreign minister Amir Khan Muttaqi be allowed to participate instead of Isaczai
The UN General Assembly drew to a close on Monday without speeches by Afghanistan or Myanmar after world powers intervened in disputes over who would represent the two countries.
The Afghan ambassador appointed by ousted president Ashraf Ghani had been due to defy the Taliban with an address at the meeting that saw 100 leaders gather in New York despite coronavirus fears.
But Ghulam Isaczai's name was removed from the list of speakers on Monday in a move that diplomats suggested had been brokered by Washington, Beijing and Moscow after they did the same for Myanmar.
"I imagine" that there was an agreement struck by those three powers, an ambassador with a Security Council country told AFP.
Another diplomat, speaking on condition of anonymity, described it as a "wise decision."
Last week, the Taliban wrote a letter to UN Secretary-General Antonio Guterres requesting that its new foreign minister Amir Khan Muttaqi be allowed to participate instead of Isaczai.
The group said that Isaczai, who had urged nations to "unequivocally state" that they would not recognize a Taliban government, "no longer represents" Afghanistan at the global body.
But diplomats at the UN said the request had come too late and Isaczai, still considered the head of Afghanistan's mission by the UN, appeared on a list of speakers sent out on Sunday.
"The country withdraws its participation in the general debate," Monica Grayley, a spokeswoman for the assembly's president, told AFP, adding that the mission had not cited a reason for pulling out.
The withdrawal came after a high-level UN diplomat told AFP that an agreement had also been reached between the United States, Russia and China preventing Myanmar's UN ambassador -- an outspoken supporter of the democracy movement -- from speaking.
Kyaw Moe Tun, chosen by former leader Aung San Suu Kyi, has defied the military junta running the country to stay in his post.
He is supported by the international community and has retained his seat at the United Nations following the February 1 military coup.
In May, the junta appointed a former general to replace him, but the United Nations has not yet approved the appointment.
Kyaw Moe Tun was the victim of a recent alleged conspiracy foiled by US investigators that plotted to either force him to resign or kill him if he refused.
He told AFP his plans for the General Assembly were "low profile."
The assembly is expected to be asked to vote in November on which of the competing delegations represent Afghanistan and Myanmar at the UN.
Guinea's representative Aly Diane, appointed by former president Alpha Conde, who was deposed in a military coup earlier this month, said the new military authorities plan to form a "government of national unity" and draft a new constitution before holding "free and fair elections."
"Arrangements have been made to allow political parties and civil society to operate freely," he said, noting that Conde's opponents have also been released.
It was another of several anomalies at the diplomatic marathon, which saw 100 leaders and dozens of ministers descend on the UN headquarters after last year's event was mostly virtual.