Shipping company Maersk confirmed in a statement on Monday that its merchant vessel Maersk Hangzhou was attacked on Saturday in the Red Sea, prompting US helicopters to respond to its calls for help by sinking three Houthi vessels and killing those on board.

It was the first time vessels have been sunk since tensions flared in the Red Sea a few months ago and the US killed members of the Iran-backed Houthi rebel group, which targets merchant ships.

The attack occurred as the Maersk Hangzhou was passing through the Bab al-Mandab Straits en route from Singapore to Port Suez.

The ship was initially “struck by an unknown object” but was able to continue moving as no fire broke out, the company said. Four vessels then approached the vessel and attempted to board the vessel according to Maersk.

“A helicopter was raised from a nearby naval vessel and, in cooperation with the vessel’s security team, the boarding attempt was successfully repelled,” the company said in a statement.

He added that Maersk Hangzhou’s crew is safe and that the company is working to assess the security of the area with Operation Prosperity Guardian — a multinational shipping coalition created to increase security in the area.

“US Navy helicopters returned fire in self-defense, sinking three of the four small boats and killing the crews. The fourth vessel escaped the area,” the statement continued, concluding that “there was no damage to U.S. personnel or equipment.”

The giant Danish shipping company Maersk announced yesterday that it is suspending for 48 hours the passage of its fleet through the strategically important Bab el-Madeb strait in the Red Sea, following the double attack by Yemen’s Houthi rebels.