Rescuers pulled six crew members alive from the Red Sea after Houthi militants attacked and sank a second ship this week, while the fate of another 15 was unknown after the Iran-aligned group said they held some of the seafarers.

Rescuers launched a search Wednesday for survivors of a Liberian-flagged cargo ship that came under attack from Yemen's Houthi rebels in the Red Sea, authorities said. At least three mariners were killed and two were wounded.

Yemen’s Houthi militants sank two commercial ships and killed sailors during three days of attacks in the Red Sea this week — a stark reminder to vessel owners and crews of the risks of traversing the maritime chokepoint.