The U.S. warned it was considering “all appropriate responses” after Houthi rebels attacked three commercial vessels in the Red Sea on Sunday, ramping up its rhetoric as Iran-backed militants continue to harass American and international interests in the region.

Following the attacks, a U.S. warship operating nearby responded to the distress calls from the commercial ships, shooting down three aerial drones over the course of the day, U.S. Central Command said in a release.

While Defense Department officials said they did not believe the militants were targeting the U.S. warship — the Arleigh Burke-class destroyer USS Carney — the string of attacks on the commercial vessels “represent a direct threat to international commerce and maritime security,” Central Command said.

While the attacks were carried out by Houthis, the U.S. has “every reason to believe” they were “fully enabled by Iran,” according to the release. “The United States will consider all appropriate responses in full coordination with its international allies and partners.”

The language is an explicit threat to Iran that the U.S. may retaliate to the attacks, which are just the latest in the region in recent weeks. Iran-backed militants have also attacked U.S. troops in Iraq and Syria at least 74 times since Oct. 17.

Sunday saw a total of four attacks against three separate commercial vessels linked to 14 separate nations, Central Command said. The Carney, which was conducting a patrol in the Red Sea, responded to the ships’ distress calls, shooting down three drones in total.

At 9:15 a.m. local time, the Carney detected an anti-ship ballistic missile fired from Houthi-controlled areas in Yemen targeting the M/V Unity Explorer, a Bahamian-flagged, UK-owned and operated bulk cargo ship. The missile came down “in the vicinity of the vessel.”

Then at 12 p.m., the Carney shot down a drone launched from Yemen. While the drone was headed toward the ship, Central Command said it “cannot assess at this time” that the Carney was the target. There was no damage to the vessel or injuries to its crew.

At 12:35 p.m., the Carney responded to a distress call from the Unity Explorer, which reported it was struck by a missile fired by the Houthis. While assisting with the damage assessment to the commercial ship, the Carney detected a second drone, and took it down.

At 3:30 p.m., the M/V Number 9, a Panamanian-flagged, Bermuda and UK-owned and operated bulk carrier, was then struck by a missile fired by the Houthis while operating in the Red Sea.

An hour later, at 4:30 p.m., the M/V Sophie II, a Panamanian-flagged bulk carrier, crewed by sailors from eight countries, sent a distress call saying it was struck by a missile. While en route to respond, the Carney shot down another aerial drone headed in its direction.

Commercial shipping has increasingly come under assault in the Red Sea since the Israel-Hamas conflict kicked off on Oct. 7.

The Carney has shot down multiple Houthi-launched cruise missiles and drones targeting commercial vessels in recent weeks. Although DOD officials do not assess the U.S. ship was the target of any of the attacks, the commander deemed some of them a threat and acted in self-defense.