American military officials said Sunday that their forces shot down two anti-ship ballistic missiles fired toward a container ship by Yemen’s Houthi rebels in the Red Sea. Hours later, four boats tried to attack the same ship, but U.S. forces opened fire, killing several of the armed crews, the U.S. Central Command said. No one was injured on the ship.

The Singapore-flagged Maersk Hanzghou reported it had already been hit by a missile Saturday night while transiting the Southern Red Sea and requested assistance, Centcom said in a statement. The USS Gravely and USS Laboon responded to the call for help, and the Denmark-owned vessel was reportedly seaworthy and no injuries were noted, the statement added.

“This is the 23rd illegal attack by the Houthis on international shipping since November 19,” Centcom said.

In another statement, Centcom said the same ship issued an additional distress call about a second attack “by four Iranian-backed Houthi small boats.” The attackers fired small arms weapons at the Maersk Hanzghou, getting to within about 65 feet of the vessel, and attempted to board it, Centcom said.

A contract-embarked security team on the ship returned fire, the central command said. Helicopters from the USS Dwight D. Eisenhower aircraft carrier and Gravely responded to the distress call and while issuing verbal warnings to the attackers, the small boat crews opened fire on the helicopters using small arms, the statement said.

“The U.S. Navy helicopters returned fire in self-defense,” sinking three of the four boats, killing the crews while the fourth boat fled the area, Centcom said, and no damage to American personnel or equipment was reported.

The Iran-backed Houthis have claimed attacks on ships in the Red Sea that they say are either linked to Israel or heading to Israeli ports. They say their attacks aim to end Israel’s air-and-ground offensive targeting the Gaza Strip following the attack by Hamas on October 7.

On Saturday, the top commander of American naval forces in the Middle East said Houthi rebels have shown no signs of ending their “reckless” attacks on commercial ships in the Red Sea even as more nations join the international maritime mission to protect vessels in the vital waterway and trade traffic begins to pick up.

Since the Pentagon announced Operation Prosperity Guardian to counter the attacks just over 10 days ago, 1,200 merchant ships have traveled through the Red Sea region, and none has been hit by drone or missile strikes, Vice Admiral Brad Cooper said in an Associated Press interview.