WASHINGTON – A senior Pentagon official told a Senate committee Thursday that the United States will be at war with al-Qaida for 15 to 20 more years and said the military could target terrorists anywhere under a law passed after the Sept. 11 terrorist attacks.

Michael Sheehan, assistant defense secretary in charge of special operations, said the battle with terrorist groups spanned the globe “from Boston to the FATA,” meaning Pakistan’s tribal areas.

Sheehan and the Pentagon’s top lawyers told the Senate Armed Services Committee that the military was authorized to target al-Qaida operatives in countries where drone strikes don’t now occur, including Mali, Syria and anywhere a host government is “unwilling or unable” to prevent al-Qaida-linked terrorists from operating on its territory.

That expansive view drew sharp criticism from some senators, who questioned how a 2001 law that authorized use of force against the organizers of that year’s Sept. 11 attacks is now used to authorize drone strikes against militants in Somalia and Yemen who played no role in those events.

“This is the most astounding and the most astoundingly disturbing hearing that I’ve been to since I’ve been here,” said Sen. Angus King, I-Maine, who caucuses with Democrats.

“You guys have essentially rewritten the Constitution here today,” King said.