Gen. David H. Petraeus told troops that the combined Afghan and U.S. forces “did tremendous work in 2010.”

The commander of the International Security Assistance Forces reminded troops in a letter dated Tuesday that the work is far from over.

“As you will recall, our core objective here is to ensure that Afghanistan never again becomes a sanctuary for Al Qaeda or other trans-national extremists,” Petraeus wrote. “Achieving that objective requires that we help Afghanistan develop the ability to secure and govern itself. This, in turn, requires the conduct of a comprehensive civil-military campaign, carried out in full partnership with our Afghan counterparts, to improve security, develop Afghan security forces, and support the establishment of good governance and economic development.”