The United Nations recorded 2,730 dead and 5,169 injured in attacks in the first 11 months of this year, Jan Kubis, UN special representative to Afghanistan, told the UN Security Council.
The figure is 10 per cent higher than for 2012, he added. A recent UN report said half of the casualties were caused by roadside bombs and suicide bombers.
"It is civilians that continue to bear the brunt of the conflict," Kubis said, highlighting that armed opposition groups such as the Taliban are responsible for most of the dead.
The 46,000 US and 27,000 troops from other foreign states are gradually leaving Afghanistan as part of a withdrawal to be completed by the end of 2014.
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But President Hamid Karzai has frustrated western nations by refusing to sign a security accord with the United States to allow military assistance from 2015.
Kubis said leaders of neighbouring countries had expressed concern about the uncertainty and "the potential for volatility post-2014 if there is a vacuum which could encourage the spread of Al Qaeda-linked international terrorism."
"An agreed bilateral security agreement between Afghanistan and the US is a precondition for an Australian commitment post-2014," said Gary Quinlan UN ambassador for Australia whose final troops left Afghanistan this month.
Envoys also expressed concern about a surge in opium production in Afghanistan and indicated caution over presidential and provincial elections to start in April.