Yemen’s Houthi rebels attacked a merchant ship in the Red Sea on Wednesday in the latest escalation of the Iran-backed militia’s campaign against shipping in support of Palestinians in the Gaza Strip.

A British government maritime agency said the vessel was “hit on the stern by a small craft” about 66 nautical miles southwest of the Houthi-held port of Hodeida in Yemen.

After the attack, the ship was “taking on water, and not under command of the crew,” the agency, The United Kingdom Maritime Trade Operations, said in a statement on its website. The statement said the ship’s master had reported it was also “hit for a second time by an unknown airborne projectile.”

A Houthi military spokesman, Yahya Saree, said in a televised speech that the group had used unmanned surface boats, a number of drones and ballistic missiles to target the ship, which he identified as the Tutor, a Greek-owned bulk carrier. He claimed the ship was seriously damaged and could sink.

On Wednesday, the Houthis said they launched two joint military operations with the Islamic Resistance in Iraq, on the Israeli cities Ashdod and Haifa, a claim Israel denied.

Since November, the Houthis have launched dozens of attacks on ships in the vital sea route in the Red Sea and Gulf of Aden, stifling global maritime trade.

In retaliation, the U.S. and British navies have been intensifying airstrikes against Houthi targets, the latest coming on June 7 after the rebel group detained 11 United Nations employees in Yemen.

The U.S. Central Command said its forces had destroyed four aerial drones and two anti-ship missiles in Houthi-controlled areas of Yemen last Friday, as well as a Houthi patrol boat in the Red Sea.

In February, American military officials said the United States struck five Houthi military targets, including an undersea drone they described as an “unmanned underwater vessel that they believed the Houthis could have received from Iran.