Afghan President Hamid Karzai has told a meeting of political leaders they should support a security pact with the US, but acknowledged there was little trust between the two nations.

The Loya Jirga, or grand council, convened a day after Mr Karzai and Washington reached agreement on a pact defining the shape of the US military presence after a 2014 drawdown of multinational NATO force.

"My trust with America is not good. I don't trust them and they don't trust me," Mr Karzai said.

"During the past ten years I have fought with them and they have made propaganda against me."

The five-day Loya Jirga will now debate the draft and decide whether US troops will stay or leave Afghan forces to fight the Taliban insurgency alone.

For almost a year, Washington and Kabul have struggled to conclude a Bilateral Security Agreement that will help determine how many US soldiers and bases remain in Afghanistan after most foreign combat troops exit by the end of next year.

The Taliban has condemned the traditional Loya Jirga as a farce.

Insurgents fired two rockets at the tent where the previous Loya Jirga was last held in 2011, but missed the delegates.

The Afghan tribal elders and political leaders, who have travelled from all over the country to attend the grand assembly, have voiced frustration over the way negotiations between Kabul and Washington have been conducted.

The draft agreement is to take effect on 1 January 2015, and says it will remain in effect "until the end of 2024 and beyond, unless terminated".

A senior US administration official said there has been no decision on the size of any post-2014 US force, however the administration does not foresee a residual force staying in Afghanistan until anywhere near 2024.

Efforts to finalise the pact stalled on Tuesday amid disagreement over whether US President Barack Obama had agreed to issue a letter acknowledging mistakes made during the 12-year Afghan war.

US Secretary of State John Kerry denied any discussion about the possibility of a US apology to Afghanistan for US mistakes or Afghan civilian casualties, a move that would likely draw widespread anger in the United States.

"The important thing for people to understand is there has never been a discussion of or the word 'apology' used in our discussions whatsoever," Mr Kerry said, adding that President Karzai had also not asked for an apology.

It was unclear where the notion of an apology originated.

A US official said that when Mr Kerry declined Mr Karzai's invitation to attend the Loya Jirga, the Afghan leader asked for US reassurances to the council on the future security relationship that would also address civilian casualties.

Mr Kerry suggested outlining the US position in a letter. When Mr Karzai asked if the letter could come from Mr Obama, Mr Kerry said he would check, the official added.

Yesterday, Mr Kerry said: "It is up to President Obama and the White House to address any issues with respect to any possible communication" between the two presidents.

Susan Rice, Mr Obama's national security adviser, insisted on Tuesday that an apology was "not on the table".

US forces arrived in Afghanistan soon after the 11 September 2001 attacks on New York and Washington and toppled its Taliban-led government, which harboured al-Qaeda leaders.

Their presence has generated deep enmity among some Afghans, who resent what they see as US violations of their sovereignty and civilian casualties flowing from US military operations.

The drawdown of Western troops has allowed tentative peace overtures between Kabul and the Taliban to gather pace, and Afghan officials arrived in Pakistan yesterday to initiate talks.