US Secretary of State John Kerry has arrived unannounced in Kabul to try to advance troubled negotiations on some US troops staying in Afghanistan after 2014.
President Hamid Karzai said this week he was prepared to walk away from the Bilateral Security Agreement (BSA) talks if Afghanistan was not happy with its conditions.
But the United States has repeatedly pressed for the pact to be signed by the end of this month so the US-led NATO military coalition can schedule its withdrawal of 87,000 combat troops by December 2014.
"President Obama and President Karzai reaffirmed both back in January that the goal here was to complete the BSA in October," a state department official travelling with Kerry told reporters on Friday.
"We continue to believe that is both preferable and doable. It is only October 11 at this point and obviously it is desirable.
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"Uncertainty about an incomplete BSA could erode the resolve among NATO allies: makes (it) more difficult to plan for the US, makes (it) more difficult to plan for our NATO allies. The goal has not changed and that is what we continue to press for."
Karzai said he refused to be rushed into signing the deal and would first seek approval from a traditional grand assembly to be convened in about month's time.
"If it doesn't suit us and if it doesn't suit them, then naturally we will go separate ways," Karzai said in a BBC interview in Kabul broadcast on Monday.
The agreement would see a few thousand US troops remain in Afghanistan to train local forces and target al-Qaeda remnants.
According to the Afghan government, talks ground to a halt over US demands for the right to conduct unilateral military operations, and on how the US would protect Afghanistan.
The collapse of a similar agreement with Iraq in 2011 led to the US pulling troops out of the country, which is currently suffering its worst sectarian violence since 2008.
But Kabul has dismissed the possibility the US may enact the "zero option" of a complete pull-out after its troops have fought the Taliban for 13 years since the 9/11 attacks in 2001.
"The BSA negotiations have been going on for 11 months. We are at a pivotal period," the US official with Kerry said.
"We will be discussing where we are and see to continue to make progress. Negotiations were ongoing before we arrived and will be ongoing after we depart from Kabul. So that is not the expectation in terms of conclusion."
