A row between the US and Pakistan over supply routes to Afghanistan is threatening to overshadow the summit of Nato leaders in Chicago.
The two sides have been unable to reach agreement on Pakistan’s conditions for reopening the routes, closed after a US air strike killed many troops.
The summit goes into a second day with troop withdrawals from Afghanistan dominating the agenda.
France insists that its troops will return by the end of 2012.
President Francois Hollande said the issue was “non-negotiable because it was a question of French sovereignty”.
The handover is expected to be completed by 2014, but several other Nato leaders are under domestic political pressure to bring troops home earlier.
More than 50 leaders are attending the summit, including heads of state and government from the 28 Nato countries, along with Afghan President Hamid Karzai and Pakistani President Asif Ali Zardari.
The summit is expected to endorse plans to hand over combat command to Afghan forces by mid-2013 and seek progress in opening routes for troop withdrawals.
They also hope to reach a commitment on who pays how much towards funding Afghan forces after 2014.
Some nations – including the US, Australia, Britain, and Germany – have pledged to contribute to an international fund to help Afghan forces after the Nato pullout.
Washington is expected to pay half of an estimated $4bn (£2.5bn) needed every year.
The US invited Mr Zardari to the summit, in the hope of signing a deal to reopen the Pakistan-Afghanistan border to US transport.
The route was closed in November after a US drone attack killed several Pakistani troops.
But in return for reopening the routes, Pakistan has called for:
- A public apology for the killings
- A review of US policy on drone attacks inside Pakistan
- An increase of the transit charge from $250 (£158) to $5,000 per vehicle.
US Defence Secretary Leon Panetta said before the summit that it was “not likely” that the US would be prepared to pay the higher amount demanded by Pakistan.
Correspondents say US President Barack Obama is unhappy about the fee, given that US is already giving Pakistan large amounts of aid.
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