Pakistani officials have complained publicly about the attacks from unmanned U.S. aircraft in tribal areas, saying they are a violation of sovereignty and increase resentment towards both Pakistan's government and the United States.

U.S. officials normally decline to comment publicly on reports of the missile strikes, but Gates made an exception when asked about Pakistan's complaints at a hearing of the Senate Armed Services Committee.

U.S. drones fired missiles into the northwestern regions of North and South Waziristan late on Friday, killing 17 people, according to intelligence officials and residents, in the first such strike since Barack Obama became U.S. president, succeeding George W. Bush.

"Both President Bush and President Obama have made clear that we will go after al Qaeda wherever al Qaeda is and we will continue to pursue that," Gates said.

Asked by committee chairman Senator Carl Levin, a Michigan Democrat, if that decision had been conveyed to the Pakistani government, Gates replied: "Yes, sir."

The United States, frustrated by an intensifying Afghan insurgency and what it sees as Pakistan's failure to stem the flow of al Qaeda and Taliban fighters from northwest Pakistan into Afghanistan, stepped up the missile attacks last year.

It has carried out about 30 missile attacks, according to a Reuters tally, more than half of them in the last four months of the year.