WASHINGTON — The United States will act against Iran if all efforts to end its suspected nuclear weapons program fail, Defense Secretary Leon Panetta said.

“Military action is the last alternative when all else fails,” he said Tuesday, the last day of the annual policy conference of the American Israel Public Affairs Committee. “But make no mistake, if all else fails, we will act.”

Panetta’s pledge was the most explicit by an Obama administration official warning of military action.

Panetta spoke after he and President Obama met with Israeli Prime Minister Benjamin Netanyahu in a bid to coordinate strategy on Iran.

The talks ended with disagreements still in place over how soon Iran’s reported advances would merit a strike.

Panetta pleaded for close cooperation with Israel.

“The United States must always have the unshakeable trust of our ally Israel,” he said. “We are stronger when we act as one.”

He underscored the U.S. commitment to keeping Iran from acquiring a nuclear weapon.

“No greater threat exists to the security of Israel, to the entire region, and indeed to the United States than a nuclear-armed Iran,” he said.