About 3,000 Afghan tribal elders and civil leaders will gather in Kabul next month to decide the fate of a deal allowing some US troops to stay in the country after 2014, officials said.
Organisers of the "loya jirga" said that leaders of the Taliban would be welcome to attend the event, due to take place between November 18-21.
The meeting will either accept or reject the Bilateral Security Agreement (BSA) that has already been the subject of months of negotiations between Afghanistan and the US.
President Hamid Karzai has said that only a loya jirga could pass judgment on an issue of Afghan national sovereignty, with legal immunity for US troops remaining a potential sticking point in discussions.
"We expect around 3,000 representatives to attend the jirga," Sadeq Modabir, a member of the organising committee, said. "It may last between four and seven days."
"If the Taliban announce that they will send representatives, we welcome them," he added, in line with government policy to open communication with the fighters.
The US secretary of state, John Kerry, visited Kabul a week ago to try to confirm the BSA after Karzai threatened to abandon negotiations. The sides agreed on a text that could be taken to the loya jirga for approval, after which it would go before the Afghan parliament.
No progress made
In 2011, a loya jirga to discuss the strategic partnership deal decided that Afghan security forces should lead all military operations, the Afghan air force be better trained and US troops on Afghan soil should not receive immunity.
If the loya jirga and parliament pass the new BSA text, between 5,000 and 10,000 US troops would stay in Afghanistan to train the national army and fight armed groups opposed to the government.
The US had been pushing for the BSA to be signed by the end of October to allow the NATO coalition to plan the withdrawal of its 87,000 combat troops by December 2014.
The collapse of a similar security agreement with Iraq in 2011 led to the US pulling its troops out of the country, which is currently suffering its worst sectarian violence since 2008.
Afghan officials always dismissed the possibility that the US could enact the "zero option" of a complete pull-out.