A resolution unanimously backed by the 15-nation council authorised the International Security Assistance Force (ISAF) to "take all necessary measures" to carry out its duties until December 31, 2014.
The United States and other western nations -- who have been in Afghanistan since just after the September 11, 2001 attacks -- say they will hand over all security duties to Afghan forces by the end of next year.
While western countries remain nervous about Afghanistan's future, they have already started to withdraw troops while still battling the Taliban.
ISAF has had rocky relations with President Hamid Karzai's government, but troop numbers are steadily falling.
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A security deal to allow some US troops to stay in Afghanistan to fight Al-Qaeda appeared at risk of collapse after Karzai threatened to walk away from negotiations.
According to the Afghan government, talks ground to a halt over US demands for the right to conduct unilateral military operations after 2014.
The United States has pushed for a bilateral security pact to be signed by the end of this month so the ISAF withdrawal can remain on schedule.
The UN Security Council did not specifically say there would be no new mandate. But its resolution, drafted by Australia, said ISAF's "final report in December 2014 should be a comprehensive one."
The resolution highlighted international support for Afghanistan after 2014 but also Afghanistan's promises at international conferences to improve its electoral organization ahead of a presidential vote in April.