Afghan President Hamid Karzai on Saturday signalled that a deal to allow US troops to stay in Afghanistan was close to collapse as the NATO combat mission withdraws after a decade of fighting the Taliban.

The Afghan president says he will not sign a security pact with the US unless Washington and Pakistan launch a peace process with Taliban insurgents.

Late last year, Karzai made a surprise decision not to promptly sign the bilateral security agreement (BSA) with the US, despite a "loya jirga" national assembly voting for him to do so.

Washington has become increasingly frustrated by Karzai´s manoeuvreing over the deal, stressing that negotiations were completed in November and that it is ready to sign the mutually agreed text.

"Afghanistan will absolutely not accept or sign anything under pressure," Karzai told reporters in Kabul. "If they want to leave, then they go and we will continue our lives... Our main condition is the practical start of peace process. "The US had earlier pushed for the BSA to be signed by the end of October so that the NATO military coalition could schedule the withdrawal of its troops by the end of this year.

But the deadline has slipped as Karzai refused to sign and even suggested that his successor could make the final decision after presidential elections due on April 5.

Karzai on Saturday repeated that before he signs the BSA, the US must foster a genuine peace process with the Taliban militants and also stop military operations. "The start of a peace process would mean that no foreigners can benefit from the continuation of war," Karzai said.

About 58,000 NATO-led combat troops still in Afghanistan are due to leave by the end of 2014.Washington is proposing about 10,000 US soldiers are deployed from 2015 to train and assist Afghan security forces in their battle against the Taliban militants.

A Taliban office in Qatar that opened last June was meant to lead to peace talks, but instead it enraged Karzai after it was styled as an embassy for a government-in-exile. Afghan officials dismiss the possibility that the US may enact the "zero option" of a complete troop pull-out as it did in Iraq, which is currently suffering a surge in bloody sectarian violence.