Top U.S. officer in Pakistan on unannounced visit

WASHINGTON (Reuters) - The top U.S. military officer, Adm. Mike Mullen, went to Pakistan on Tuesday for an unannounced visit amid stepped-up U.S. efforts to combat militants operating along Pakistan's border with Afghanistan.

The trip by Mullen, chairman of the U.S. Joint Chiefs of Staff, comes as Pakistani government leaders protest American military operations in the region, including a suspected U.S. commando raid this month.

"The chairman is in Pakistan today for meetings with senior civilian and military leaders," said Navy Capt. John Kirby, spokesman for the chairman of the U.S. Joint Chiefs of Staff.

"He'll meet with Prime Minister (Yousaf Raza) Gilani and the chief of army staff, General (Ashfaq) Kayani, to continue the dialogue that they have been maintaining and to look for ways to work better and more closely together to eliminate the safe havens for extremists in the border region."

U.S. officials say Taliban and al Qaeda-linked fighters use the tribal regions along Pakistan's side of the border as an operating base to launch attacks inside Afghanistan.

Targeting those safe havens is one of Mullen's top priorities, his aides say, as frustration grows in Washington that Islamabad has not done enough to clamp down on fighters in the remote region.

"There are things being done. Progress is being made. There's a lot more that has to be done," a senior U.S. military officer said, speaking on condition of anonymity.

(Reporting by Kristin Roberts, Editing by Doina Chiacu)