KABUL (AFP) - US Secretary of State John Kerry landed in Afghanistan on Monday for an unannounced visit, with relations badly frayed by Kabul's recent hostility to US-led military efforts in the country.

Mr Kerry is likely to face a testing meeting with President Hamid Karzai who has launched a series of verbal assaults on US troops and their coalition partners.

"He will make clear that the US will have an enduring commitment in Afghanistan that will last beyond transition and that there will always be bumps on the road," a US official travelling with Mr Kerry told reporters.

More than 11 years after the Taleban were ousted from power, international forces are withdrawing from Afghanistan and handing responsibility for fighting the Islamic insurgents to poorly-trained local police and army.

As the transition gathers pace, the United States and Afghanistan are also negotiating a strategic pact that will determine the US presence in the country after the end of international combat operations next year.

One major cause of friction between Washington and Kabul was solved hours ahead of Mr Kerry's arrival when a ceremony was held to mark the final transfer of the controversial Bagram jail from US to Afghan control.

The drawn-out war is increasingly unpopular in the US, and Mr Karzai triggered fury earlier this month when he accused the US of working in concert with Taleban militants to justify keeping soldiers on foreign soil.

"Issues of security and sovereignty are always going to be difficult," the US official travelling with Mr Kerry said.

"But the most important thing is that we are honest to each other when there are differences between us, and you have seen some differences playing out recently."