British General David Richards' call for increased troops echoes comments by U.S. commanders made earlier in January.
Richards, who commands NATO's International Security Assistance Force (ISAF), made his comments in an interview with "The Guardian" newspaper.
Richards said it would be a "dangerous assumption" for NATO to believe the risk level of 2006 will remain the same in 2007.
He said that not only must the military apply more energy to the effort, but civilian agencies must also "improve the speed and scale" of reconstruction efforts.
About 40,000 foreign troops are in Afghanistan, some 33,000 of them under NATO command.
U.S. Defense Secretary Robert Gates has said he will consider increasing the number of U.S. troops in Afghanistan, where U.S. commanders say they expect the Taliban insurgency to intensify.
Afghan President Hamid Karzai on January 21 accused "certain Pakistani circles" of protecting insurgents fighting in Afghanistan.