An unusually large barrage of missiles fired by remotely piloted U.S. aircraft killed 16 people in the tribal area of North Waziristan on Thursday, a possible indication that the United States plans to escalate such attacks after Pakistan declined to step up its operations there.

The attacks came in a week in which top U.S. military officials visited Islamabad and asked Pakistani authorities to do more to go after insurgent groups that are based in North Waziristan but are focused on killing U.S. troops across the border in Afghanistan.