His spokesman Aimal Faizi stuck to that stance on Friday despite U.S. pleas, saying "there is no deadline for us except what the president said in his speech."
The Obama administration has said it will pull all its forces out of Afghanistan without a security deal, as it did when Iraq failed to sign a similar agreement. U.S. Secretary of State John Kerry called Karzai on Friday and warned that "further delay is not practical, nor is it tenable," State Department spokeswoman Jen Psaki said.
"Failure to conclude (the deal) ... would be seen as a signal to the world that Afghanistan is not committed to a partnership with its supporters and that it is willing to jeopardize all of the financial and practical help that has been offered," Psaki said.
The U.S. invaded Afghanistan following the Sept. 11, 2001, terrorist attacks to go after al-Qaida, which was being sheltered by the Taliban. The longest and costliest war in U.S. history has proven deeply unpopular at home and among its allies, who also have said they will not commit any troops after 2014 unless the security deal is signed.
The exit of all foreign forces would jeopardize the more than $8 billion that has been pledged annually to fund Afghan security forces and help with the country's development.
Underscoring that point, U.S. Defense Secretary Chuck Hagel said Friday he can't recommend that President Barack Obama continue planning for a post-2014 force in Afghanistan unless Afghan leaders promptly sign the security agreement.
Hagel said that without an agreement the U.S. will have no clear understanding of what the Afghan people want, what an acceptable role for U.S. forces will be or how to carry out that mission. He was speaking to reporters before the start of a security forum in Halifax, Nova Scotia.
According to a senior U.S. defense official, Hagel spoke by phone with Marine Gen. Joseph Dunford, the top U.S. and coalition commander in Afghanistan, to receive an update on the Loya Jirga and ongoing discussions with the Afghan government on the bilateral security agreement.
The official said Dunford told Hagel that Washington has sent a strong message to the Loya Jirga that the agreement must be approved now and signed without delay if Afghans want the U.S. and its allies to remain after 2014.
The official was not authorized to discuss the private conversation publicly, so spoke on condition of anonymity.
Kerry and Karzai agreed earlier this week to the language of the agreement, which would remain in force until the end of 2024 and beyond, unless terminated by mutual agreement or by either party with two years' written notice.
The draft agreement gives the U.S. legal jurisdiction over troops and Defense Department civilians who may get in trouble, despite deep divisions in Afghanistan over whether the Americans should have immunity. It also addresses the contentious issue of night raids, saying "U.S. forces can only enter Afghan homes in extraordinary circumstances when the life or limb of Americans is at stake."
The 2,500 delegates broke into small groups for closed-door meetings on whether to endorse the deal and will give their decision to Karzai on Sunday.
The assembly is widely expected to approve the agreement, and Karzai's remarks could be seen as last-minute move to force the gathering to ask him to sign the long-delayed accord thus shifting the responsibility for the deal away from him to the elders. Karzai is barred by the constitution from seeking a third term. Afghan experts in the U.S. also suggested that Karzai might be trying to pressure the U.S. into making more concessions.
Military leaders in the U.S. and NATO widely acknowledge that the nearly 350,000-member Afghan National Security Forces are not yet ready to take on the Taliban alone after a war that has lasted more than 12 years. The Afghan forces, however, have held their ground this summer after taking control of security around the country from foreign forces.
Senior U.S. military officials have repeatedly stressed that Afghan forces still need at least three to four years of training and mentoring take on a resilient Taliban insurgency that shows no sign of abating or compromising. U.S.-backed attempts to start peace talks with the Taliban have failed so far.
A signed accord means that about 8,000 U.S. troops could stay for another 10 years, which is the duration of the Bilateral Security Agreement. Although their main role will be to train and assist the Afghan military and police, a small number of U.S. forces will continue to hunt al-Qaida members.
While the agreement allows for a decade-long, if not longer, presence for U.S. troops, they may not be there over that period. The Obama administration has yet to specify how long U.S. troops might actually remain to complete the training and support mission, and the agreement extends far past Obama's tenure as president.
U.S. officials have not yet disclosed how many troops they want to keep in Afghanistan after 2014, but they have said the number of U.S. and NATO troops could be between 8,000 and 12,000. Of those, the U.S. is expected to provide no more than 8,000.