A cargo ship was attacked in the Red Sea off the coast of Yemen, the UK Maritime Trade Operations (UKMTO) said on Sunday.

UKMTO reported that a vessel triggered a distress alert stating it was under attack by unknown armed assailants. The incident was reported around 30 nautical miles (about 55.6 kilometers) southwest of Hodeida, which is under the control of Iran-backed Houthi rebels.

UKMTO said a small boat (described as a skiff) approached the bulk carrier and opened fire, prompting the ship’s security guards to return fire. The skiff then sailed back to a larger ship about 2 nautical miles away.

No group immediately claimed responsibility for the attack.