The U.S. military strikes against targets in southern Iran on Monday came after intelligence analysts detected a series of potentially threatening Iranian military actions in the 24 hours leading up to the strikes, two American officials said on Tuesday.

American warplanes sank two of Iran’s Islamic Revolutionary Guard Corps speedboats that were trying to place mines in the Strait of Hormuz, a vital waterway that carried roughly a fifth of the world’s daily oil and gas supply before the war, and that Iran has since effectively blocked.

The officials, who spoke on condition of anonymity to discuss operational matters, also said that Iran launched one-way attack drones near some of the nearly two dozen U.S. Navy warships in or around the Gulf of Oman and the Arabian Sea. The ships are enforcing a blockade against vessels trying to enter or leave Iranian ports.

U.S. military analysts also detected activity at some of Iran’s surface-to-air missile sites near the Strait of Hormuz that threatened land- and carrier-based attack planes operating in the region as part of the naval blockade.

In response, the United States carried out “self-defense strikes” against the targets in southern Iran “to protect our troops from threats posed by Iranian forces,” Capt. Tim Hawkins, a spokesman for U.S. Central Command, said in a statement on Monday.

On Tuesday, Captain Hawkins declined to comment further on the strikes, pointing to his statement on Monday that “U.S. Central Command continues to defend our forces while using restraint.”

Other Pentagon officials dismissed Iranian media reports on Tuesday that Iran had downed an American MQ-9 Reaper drone.

U.S. officials also said on Tuesday that the Revolutionary Guard Corps may have been testing to determine whether their forces have some new, additional operating room as the two sides try to solidify the potential agreement that President Trump has said could end the war and reopen the Strait of Hormuz.