(Bloomberg) -- Houthi militants are attacking commercial ships off Yemen with increasing — and sometimes deadly — effectiveness, exposing the limits of a US-led coalition to quell the violence in some of the world’s most important waterways.

The Houthis struck the commodities carrier Transworld Navigator in a suspected drone attack early Sunday, marking the fourth time the vessel has been targeted, according to US Central Command. The ship continued on its path through the Red Sea, following moderate damage and minor injuries to the crew. 

Earlier this month, a seafarer died after an attack on the Tutor, a ship hauling coal that was built in 2022. The vessel sank in what appeared to be the first successful Houthi strike from a seaborne drone.  

Since late last year, the Iran-backed Houthis have targeted merchant ships for what they say is a response to the Israel-Hamas war. But there are clear signs that — as well as stepping up attacks — the militants are doing more damage. 

In a separate recent incident, crew members on the cargo carrier Verbena abandoned ship in the Gulf of Aden following two Houthi missile attacks that caused fires on board, according to the US military. The mariners were rescued by another bulk carrier.

The recent barrage, following a lull, raises questions about whether the coalition is able to prevent the attacks in waters that in normal times are a major trade route for oil, liquefied natural gas and other commodities. Vessel traffic in the Red Sea region has dropped about 70% since December, with many commercial ships now taking the more expensive and time-consuming route around Africa.

The head of the European Union’s naval force in the region last week said it needs to double in size to effectively combat the Houthis. 

Officials from US Central Command didn’t immediately respond to a request for comment to the recent incidents on Monday.

Meanwhile, the USS Dwight D. Eisenhower aircraft carrier strike group is leaving the region as it has come to the end of its scheduled deployment. It will be replaced by the USS Theodore Roosevelt strike group. 

©2024 Bloomberg L.P.