John Sawers, Britain's envoy to the UN, denied that the resolution specifically called on countries to increase troop levels but said it urged "that efforts should be sustained and that we should have the forces there necessary to deliver on the tasks".
US and Nato casualty figures are at their highest since US-backed forces overthrew Afghanistan's Taliban rulers in 2001.
Thursday's routine renewal of the Nato-led force's mandate came on the same day that a suicide bombing outside the Indian embassy in the Afghan capital, Kabul, killed at least 17 people and injured scores.
The Taliban said it had carried out the attack, but Al Jazeera's Zeina Khodr, reporting from Kabul, said Afghan government and intelligence sources believed foreign hands were involved in the attack.
The ISAF extension also comes as Barack Obama, the US president, continues to deliberate US strategy for the war and whether to send more troops.
Obama has been holding numerous dialogue sessions with bipartisan congressional leaders as he considers a reported request by his top general in Afghanistan, Stanley McChrystal, for as many as 40,000 more US soldiers.
The US president appears to have ruled out shrinking the war to a smaller, purely counterterrorism effort, but has also indicated he will not build up US forces into the hundreds of thousands.
Reports say he is considering focusing more on fighting al-Qaeda and sharpening the distinction between it and the Taliban.
Obama, who has already added 21,000 troops to the military campaign in Afghanistan during his presidency, is under growing pressure from his political opponents and waning US public support for the war.
Saif Jawad, Afghanistan's ambassador to the US, told Al Jazeera this week that more US troops were needed in his country to help promote stability and train domestic security forces.
"If those troops do not arrive, the challenges will be even bigger and we might not have adequate [numbers] of trainers in time, to train our own security forces [in order] to take the responsibility of the fight ourselves," he said.
"If they come to Afghanistan, it will make it easier for Afghans to take the responsibilities for themselves. We are hopeful that the president [Obama] will accommodate the request that General McChrystal has put forward."