Nato warned today that an early presidential election in Afghanistan would have implications for security and said it would be in a better position to protect the poll if it were held in August.
Afghan President Hamid Karzai said on Saturday the vote should be held according to the constitution which gives the last date for an election as 21 April.
This put him on a collision course with the country's election commission which set a 20 August date and with Washington and its Nato allies, who have pledged military reinforcements to protect the process.
Nato spokesman James Appathurai told Reuters that when the election was held was an Afghan decision, but added: "The date chosen will have implications for how much capability we will be able to bring into Afghanistan to support the electoral process. "The bottom line is that we will be able to provide more support and more security for an August election than we would for an earlier one."
The surprise call for an early election was seen by analysts as a ploy to show Karzai respected a 21 May constitutional deadline to leave office - but at the same time force his opponents, none of whom are remotely ready to stand in April, to ask the president to stay on.
US President Barack Obama has ordered 17,000 more troops to Afghanistan to try to secure the election in August against a powerful and growing Taliban insurgency. Bringing the poll forward would not give the troops time to arrive in the country.
Nato has struggled to persuade its European members to provide extra troops for Afghanistan, given lack of popular enthusiasm for the conflict and arguments that European armed forces are already stretched by other commitments.
But the deputy commander of Nato's International Security Assistance Force had said last week it was confident NATO member states would provide thousands of extra troops as temporary reinforcements for an August poll.
Afghanistan will top the agenda at a meeting of foreign ministers of the 26 Nato states in Brussels on Thursday.