U.S. media report the Central Intelligence Agency is building a secret air base in the Middle East to use for armed drone attacks on terrorists in Yemen.

The Associate Press, which first reported the construction plans, quotes unnamed U.S. officials who say the base, at an undisclosed location, could be operational by the end of the year.

The building of the base comes at a time the U.S. government is increasingly worried about Yemen-based al-Qaida in the Arabian Peninsula.

The group has tried to carry out terrorist attacks on the United States and has taken control of large areas of Yemen during months of civil unrest and protests against Yemenis President Ali Abdullah Saleh.

Yemen's government has permitted some U.S. military operations in the country and is now allowing expanded strikes against al-Qaida targets.

U.S. officials say the construction of the CIA air base suggests President Barack Obama's administration views armed drones as a key weapon against terrorist targets. Drone strikes are frequently carried out in Pakistan, although the United States does not publicly acknowledge them.

There have been frequent clashes in Yemen. On Wednesday the Associated Press quoted Yemeni security officials as saying that Islamic militants seized parts of the southern city of Houta in a surprise attack.

For several months, there have been widespread protests against the 33-year reign of Mr. Saleh. The U.S. and Yemen's Gulf neighbors have tried to negotiate a deal for him to leave office, but he has refused. They now hope to insure that he does not return to his homeland from Saudi Arabia, where he is being treated for injuries from a bomb attack inside his presidential compound.

The U.S. government says the Yemen-based al-Qaida group is responsible for the attempted bombing of an airliner to Detroit on Christmas Day in 2009, as well as an effort to dispatch bomb-laden packages to the U.S. last year.