President Barack Obama has paid a surprise visit to Afghanistan and assured cheering US troops they are winning the war against the Taliban despite "difficult days ahead."
Obama landed in the country under cover of darkness on Friday, with aides announcing nothing of the trip beforehand due to security concerns. He left four hours later, in the early hours of Saturday morning.
Obama, who has tripled US troop numbers in Afghanistan, spent a mere four hours in the country during his second visit as president, both to this base outside Kabul.
A face-to-face visit with President Hamid Karzai was replaced with a 15-minute phone call, as weather scuppered plans to fly Obama by helicopter from the base to the nearby Afghan capital.
The trip came as the Obama administration faced new friction with Karzai over embarrassing assessments in leaked diplomatic cables of the Afghan leader, but war czar Douglas Lute said the topic did not come up in the phone call.
Karzai's chief spokesman, Waheed Omer, also said Karzai was "not upset" that his US counterpart and main backer had not visited him at his palace.
"President Obama was not here for a state visit but rather to visit American troops. The two leaders had already met in Lisbon two weeks ago and spoke in detail," Omer told AFP on Saturday.
"There was no special agenda for this visit," Omer said, confirming that "the two leaders did talk on the phone for 15 minutes."
At the Lisbon summit, the NATO alliance backed Obama's goal of handing over security to the Afghan police and military by mid-2011, with a view to ceding full control by the end of 2014.
Lute said that, during their Saturday phone call, Obama and Karzai "both acknowledged that early 2011 is not far off and that this has to remain a priority for both of them, to begin the transition process."
At Bagram, Obama told nearly 4,000 cheering troops that "you're achieving your objectives, you will succeed in your mission. We said we were going to break the Taliban's momentum. That's what you're doing."
But he warned "there are going to be difficult days ahead" in the fight against insurgents, and appeared to choke up as he described his visit to a base hospital where he pinned Purple Heart medals on five wounded soldiers.
A year after Obama authorized a surge of 30,000 US troops, Afghanistan is in the grip of growing violence. More than 1,400 US servicemen and -women have been killed since the 2001 US-led invasion ousted the Taliban -- a third of them this year alone.
Obama also spoke to a platoon that recently lost six of its members in an attack.
"I don't need to tell you this is a tough fight," Obama said, but stressed that "today we can be proud that there are fewer areas under Taliban control, and more Afghans have a chance to build a more hopeful future."
He noted that since his last visit, in March, the allied coalition had grown by six to 49 countries, which he called a "powerful message" of support for the war-torn nation.
"We will never let this country serve as a safe haven for terrorists who would attack the United States of America again," he added.
Sporting a leather bomber jacket, Obama was met at Bagram by US ambassador Karl Eikenberry and war commander General David Petraeus, whom Obama praised as an "extraordinary warrior."
"This is somebody who has helped change the way we fight war, and win wars, in the 21st century," he added.
After his address, Obama shook hands and took pictures with several hundred troops at a ropeline, and received a briefing from US Special Forces.
Some 100,000 US troops are fighting in Afghanistan as part of Obama's ramped-up strategy to battle insurgents, loyalists of the regime that harboured Osama bin Laden, mastermind of the September 11, 2001 terror attacks on the United States.
White House aide Ben Rhodes said the White House began preparing the Kabul visit more than a month ago as Obama wanted to visit US troops and civilians in Afghanistan between Thanksgiving and Christmas.
The trip followed the latest release by WikiLeaks, in which secret US diplomatic cables showed renewed US questions about Karzai's leadership and rising concerns about corruption.