During an unannounced visit to Bagram air base near Kabul on December 3, Mr Obama said: "Today we can be proud that there are fewer areas under Taliban control."

He said there would be "difficult days" ahead in their fight against the Taliban.

But he added: "You're achieving your objectives, you will succeed in your mission.

He also spoke to President Hamid Karzai for about 15 minutes by telephone.

The visit comes a year after Mr Obama ordered a troop "surge" in Afghanistan, but weeks after a Pentagon report found violence there at an all-time high.

The US president's national security team is to report on the new strategy later this month.

Mr Obama's trip to Afghanistan comes about one year after he announced at West Point Military Academy the US would strengthen combat troops in Afghanistan with 30,000 reinforcements.