KABUL — Under elaborate secrecy, President Barack Obama slipped into Afghanistan on Sunday near the front lines of the increasingly bloody 8-year-old war he is expanding and affirmed America's commitment to destroying al-Qaida and its extremist allies in the land where the 9-11 plot was hatched.

Obama's six-hour visit was conducted entirely under the shroud of nightfall, after Air Force One's unannounced flight from the U.S. Obama defended his decision to escalate the fight, telling troops whose numbers he is tripling that their victory is imperative to America's safety.

His bid to shore up faith in the struggle was aimed both at the troops who cheered him and Americans back home. And, he demanded accountability from Afghan authorities to make good on repeated promises to improve living conditions, rein in corruption and enforce the rule of law to prevent people from joining the insurgency.

It was Obama's first trip as president to Afghanistan, where the number of U.S. troops killed has roughly doubled in the first three months of 2010 compared with the same period last year as Washington has added tens of thousands of additional soldiers.

At least 945 members of the U.S. military have died in Afghanistan, Pakistan and Uzbekistan since the campaign started in late 2001.