Brussels - Afghanistan cannot continue stalling on a post-2014 US and Nato troop status accord without jeopardising essential financial support for its armed forces, Nato head Anders Fogh Rasmussen warned on Monday.
"The Afghan political leadership should not underestimate the negative impact [refusing to sign a deal] has... in troop-contributing countries," Rasmussen said.
If there is no agreement establishing the legal status of a US-Nato training mission after the alliance ends its combat role this year, then there is every likelihood "we will end up with the zero [troop] option".
That means a complete withdrawal - as happened with US forces in Iraq in 2011 - and no post-2014 training and advisory mission to help the Afghan military cope with what is expected to be a resurgent Taliban rebel force.
"If we do not have a troop presence in Afghanistan after 2014... it will be extremely difficult to generate financial support" for the Afghan military, he said.
At 352 000 soldiers, "I do not know how the Afghan government will be able to pay [for them]... if it does not get financial support from the financial community."
The absence of foreign troops could "also put development assistance in jeopardy", Rasmussen said, adding: "That is what is at stake for Afghan society."
Afghan President Hamid Karzai on Saturday said talks on the US-Afghan Bilateral Security Agreement (BSA) were close to collapse.
"Afghanistan will absolutely not accept or sign anything under pressure. If they want to leave, then they go and we will continue our lives," Karzai said.
Washington originally wanted the BSA signed in October to allow adequate time to plan the Nato training mission which could include up to 10 000 American troops.
Karzai refuses to sign, however, suggesting his successor should make the final decision after presidential elections on 5 April.
Karzai also insists, as he did again on Saturday, that Washington must stop military operations in the meantime and bring the Taliban to the negotiating table.
A senior Nato official said that given the apparent impasse, it was "time to be completely clear" with the Afghan government and that while there was no deadline, there was little leeway left either.