US Secretary of State John Kerry makes surprise visit to Afghanistan

US Secretary of State John Kerry arrived in Afghanistan today on an unannounced visit that is expected to address recent tensions between Washington and Kabul.

Kerry is due to hold talks with President Hamid Karzai in Kabul, where 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 told reporters.

The official acknowledged there had been "differences" lately between the US and Afghan governments — culminating in Karzai's accusation, earlier this month, that the US was colluding with Taliban insurgents to prolong instability and keep foreign forces in Afghanistan.

Kerry's delegation said "he did not plan to lecture Karzai or dwell on the apparent animosity but would make clear once again that the US did not take such allegations lightly," according to the Associated Press.

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Officials said the talks would also cover Afghanistan's elections in May, national reconciliation and the creation of a Taliban office in Qatar to host negotiations.

Karzai is due to travel to Qatar to discuss the plan, which the US supports, sometime this week.

At least one source of tension has already been resolved: shortly before Kerry's arrival, US forces transferred full control of Bagram prison to Afghan authorities, in what Afghan Defense Minister Bismillah Mohammadi called "a crucial and positive step towards the security and self-sufficiency of Afghanistan."

The handover, which has taken more than a year to complete, was the result of an agreement between the US and Afghan defense departments about the fate of detainees the US considers dangerous, but whom Kabul had indicated it would release.

Details have not been made public, but the deal is thought to say that "prisoners of concern" cannot be freed without a full review, the BBC said.

Twenty-six other prisoners were released immediately after this morning's handover ceremony.