Security has been tight in the Afghan capital as tribal elders gathered to debate a crucial pact agreed in draft form between Kabul and Washington.
The US is said to have got its way on several controversial issues concerning the conditions under which its troops may stay beyond 2014.
Intense negotiations and wrangling between both governments preceded the meeting of up to 2,500 Afghan elders at the Loya Jirga.
The accord’s implementation depends to a great extent on President Karzai.
He told the assembly his relations with America were not good. “I don’t trust them and they don’t trust me,” he said.
Recently he accused international forces of bringing only suffering to Afghanistan.
But before the Loya Jirga he said the deal was of national importance, and he called the meeting to seek political support for it.
The draft says US soldiers accused of offences in Afghanistan will be subject to US not Afghan justice.
It says US forces “shall not target Afghan civilians, including in their homes”, wording seen as granting freedom to pursue militants.
Without the accord, the American government has warned it may withdraw all its forces by the end of next year.