John Kerry in Afghanistan

Kerry and Karzai will discuss a host of issues including Afghan reconciliation, the transfer of security responsibility to Afghan forces and Afghanistan's elections, the U.S. official told reporters. Karzai's government is trying to open formal negotiations with the Taliban, who have remained resilient in the face of superior NATO firepower in the war now in its 12th year. Karzai is due to travel to Qatar within days to discuss the peace process and the opening of a Taliban office for conducting negotiations. The trip comes after years of stalled discussions with the United States, Pakistan and the Taliban. Commenting on Karzai's trip, the U.S. official told reporters: "I wouldn't want to overplay it but I think that it's a very positive sign. It's another step on a continued path toward ... getting to some sort of reconciliation process.

"Nobody is expecting that he will open an office there in a week. Nobody is expecting that he will be sitting down with Taliban in a week. This is a long process and this is one more small but positive step in that ... process."

Tensions between the United States and Afghanistan have deepened in recent years over a range of issues, including civilian casualties during air strikes, night raids and the transfer of prisoners.

The official acknowledged the difficulties in the U.S.-Afghan relationship but said he believed they had resolved a number of them, including an agreement to remove U.S. forces from part of Wardak province where they were accused of abusing local residents.

The official said Kerry had wanted to visit Pakistan on this trip but had decided not to given the May 11 election, in part to avoid any appearance of seeking to influence what would be Pakistan's first civilian to civilian electoral handover.

The military has ruled Pakistan for more than half of its 66-year history, either through coups or from behind the scenes.