Escalating Iran-backed attacks against global commercial shipping in the Red Sea have heightened pressure on the Biden administration as officials scramble to protect trade while trying to avoid a direct confrontation with Tehran.

The U.S. Navy said late Saturday that two more vessels had been attacked that day by Iranian-backed Houthi forces in Yemen, bringing the number of commercial ships attacked near a crucial passageway between the Horn of Africa and the Middle East to 15.  The Pentagon said earlier in the day that a chemical tanker in the Indian Ocean was struck by a drone launched directly from Iran, a claim Tehran denied.