By Caren Bohan
BAGRAM AIR BASE, Afghanistan (Reuters) - President Barack Obama praised American troops for "important progress" against militants in Afghanistan, during an unannounced visit to a U.S. airbase outside the capital on Friday.
A planned helicopter trip to Kabul to meet Afghan counterpart Hamid Karzai was canceled because of bad weather, and instead the two leaders spoke only briefly by telephone.
Obama's second visit to Afghanistan as president came as the White House prepared to release a review of the war strategy the week of December 13, and the day after leaked cables detailed deep concerns about Karzai's abilities and widespread fraud.
The president is under pressure to show progress in the increasingly unpopular nine-year-old war, and told nearly 4,000 troops gathered in a hangar to hear him that they were gaining ground against insurgents.
"Today we can be proud that there are fewer areas under Taliban control," Obama said, in a speech filled with tributes to sacrifices of serving troops and their families back home.
"We said we were going to break the Taliban's momentum and that's what you're doing, you're going on the offense, tired of playing defense," he said to the crowd of mostly U.S. troops.
The trip comes at a time of spiraling violence and record casualties. Altogether about 1,400 U.S. troops have died in Afghanistan since the 2001 ouster of the Taliban.
Obama last year ramped up force levels to widen the Afghan military campaign, and many of the extra troops have been thrown into tough fighting.
A major offensive in the southern Taliban heartland of Kandahar has won some ground, but the insurgency is also spreading in previously relatively peaceful northern and western parts of Afghanistan.
White House officials emphasized the main purpose of Obama's journey was a visit with the troops around the Thanksgiving and Christmas holidays, rather than a fact-finding mission ahead of the upcoming strategic review.
"I know it's not easy for all of you to be away from home especially during the holidays and I know its hard on your families, they have got an empty seat at the dinner table," Obama told the crowd, after visiting wounded soldiers.
He awarded five Purple Heart medals in the Bagram hospital.
In addition to talking to Karzai, Obama got briefings from key advisers, including General David Petraeus, the top commander of U.S. and NATO forces in Afghanistan, and Karl Eikenberry, the U.S. ambassador to Afghanistan.
Officials have said they believed NATO forces were making progress in training Afghan security forces, who will take control of security as foreign troops begin to leave.
Obama has set a mid-2011 target to start the withdrawal, and U.S. and NATO officials say they aim to complete the handover to Afghan forces by 2014, a goal set by Karzai.
Obama's Republican critics have criticized the July 2011 timeline, saying that announcing a date emboldens the Taliban.
The December review will assess and potentially recommend changes to the strategy Obama rolled out a year ago when he ordered 30,000 additional troops to that war zone, although his team says there will be no major shifts.
"This is a process which is diagnostic in nature. This is not a policy review similar to the one that was undertaken last year. We have a strategy in place," Ben Rhodes, deputy national security adviser for communications, told reporters on Air Force One ahead of the visit to Afghanistan.
"We'll assess that strategy and review the need for any adjustments but these adjustments, again, won't be of the nature of a policy overhaul."
As usual with such trips, Obama's visit was not announced previously for security reasons. He was spirited out of the White House secretly Thursday night and flew overnight aboard Air Force One for the trip to Afghanistan.
Because the planned a meeting and dinner with Karzai was canceled, the trip was shortened from six hours to three hours.
(Additional reporting by Michelle Nichols, writing by Emma Graham-Harrison; Editing by Jon Hemming)