The United States has begun launching drone strikes against suspected al-Qaeda operatives in Yemen under new authority approved by President Obama that allows the CIA and the military to fire even when the identity of those who could be killed is not known, U.S. officials said.

The policy shift marks a significant expansion of the clandestine drone war against an al-Qaeda affiliate that has seized large ­pieces of territory in Yemen and is linked to a series of terrorist plots against the United States.