CAIRO (AP) — The U.S. military announced Thursday that it is conducting the 13th night of strikes against Iran as clashes escalate over shipping routes. Earlier Yemen’s Iran-backed Houthi rebels said they attacked two Saudi oil tankers in the Red Sea, potentially widening the Iran war as international oil topped $100 a barrel.U.S. Central Command said the latest attacks are designed to “further degrade Iran’s ability to threaten civilian mariners and commercial vessels transiting regional waters” as the Americans push to regain control over the Strait of Hormuz and restore the flow of international shipping.Meanwhile, the Houthis threatened to shut down another key trade route, with the world economy already reeling from Iran’s closure of the Strait of Hormuz. The threat came as Iran and the U.S. have stepped up attacks as they vie for control of the strait, through which a fifth of the world’s oil and gas transited in peacetime, setting off a scramble for alternative routes.

President Donald Trump threatened “major military punishment” against the Houthis if their attacks on ships continue.“If they do this again, the U.S. will hold Iran responsible, in that the Houthis are a Surrogate and/or Proxy of Iran, and major military punishment will be inflicted upon Iran and, of course, the Houthis, themselves,” Trump wrote on social media.