US President Barack Obama put the fight against corruption at the top of his agenda in talks with his Afghan counterpart during a surprise visit to the country on Sunday, US officials said, dpa reported.
The visit is Obama's first since he took office in January last year.
Obama arrived on Sunday evening from Washington and was due to stay for just one day, officials said. He met immediately with Afghan President Hamid Karzai.
The fight against corruption in the Afghan government and against the illegal drugs trade, which finances rebels in the country, were the main issues discussed at talks between the two presidents, officials said.
Obama expected more progress, according to a joint statement issued after the talks and quoted by the media.
US forces have been fighting in Afghanistan since 2001. In December, Obama ordered an extra 30,000 troops to be sent to the country to strengthen the fight against the Taliban insurgency. That would bring the total number of US troops in the country to 100,000.
President Karzai's re-election last year was overshadowed by allegations of widespread vote-rigging.
"We plan to engage President Karzai," security advisor James Jones told journalists during the flight to Afghanistan, "to make him understand that in his second term there are certain things that have not been paid attention to, almost since day one.
"That is things like a merit-based system for appointment of key government officials, battling corruption, taking the fight to the narco-traffickers, which ... provides a lot of the economic engine for the insurgents," he continued.
Karzai said that he and Obama had had a "good discussion," and that he wanted to "express the gratitude of our people for the help that America has given us for the last eight years."
White House spokesman Robert Gibbs said that Karzai had been informed of the visit on Thursday. In the US, journalists had earlier been told that Obama would on Sunday be in Camp David, a military camp and presidential retreat in Maryland.
From there, the president flew out to Afghanistan. After arriving at Bagram airfield in Parvan province, he flew by helicopter to the capital Kabul.
He is later scheduled to deliver a speech in front of around 2,000 US troops, the US television station CNN reported.