Commercial ships still sailing through the Red Sea are broadcasting messages about their nationality and even religion on their public tracking systems to avoid being targeted by Yemen's Houthis after deadly attacks this week by the militia.

Videos released by Yemen’s Houthi rebels showed what it said was the sinking of two Greek-owned ships. WSJ’s Benoit Faucon explains how the attacks show that the militant group remains a potent threat.

The US has accused the Houthis of kidnapping several crew members. They were “much more aggressive” attacks than in the past, said Martin Kelly, head of advisory for maritime security experts EOS Risk Group.