Obama said difficult days lie ahead in the eight-year-old war and that there would be setbacks. But he said “the US doesn’t quit and will prevail.”

The president spoke to about 2,500 US forces at Bagram Air Field after talks in Kabul with Afghan leaders. “I promise I will never send you out unless it is necessary,” he told the troops.

Obama told President Hamid Karzai and his Cabinet that they needed to make more progress in fighting corruption and improving their government. Obama told them he was pleased with progress made since his last discussion with Karzai by secure video conference on March 15. Obama also invited Karzai to visit Washington on May 12.

He praised recent steps in the military campaign against insurgents. But in discussions that lasted about 30 minutes at the presidential palace, Obama stressed that Afghans need to see conditions on the ground get better. “Progress will continue to be made ... but we also want to make progress on the civilian front,” Obama said, referring to anti-corruption efforts, good governance and adherence to the rule of law. “All of these things end up resulting in an Afghanistan that is more prosperous and more secure,” he said after a brief meeting with Karzai.

Karzai promised that his country “would move forward into the future” to eventually take over its own security, and he thanked Obama for the American intervention in his country.

He told Obama he has begun to establish more credible national institutions on corruption and made clear he intends to make ministerial appointments more representative of the multiple ethnic and geographic regions of the country, according to a US account.

Obama had gone on Friday afternoon to the presidential retreat at Camp David, Md., from which unnoticed departures are easier because of its secluded mountain location. The small contingent of White House aides and media allowed on the trip were sworn to secrecy.