WASHINGTON — Yemen’s Houthi rebels seized the high ground overlooking the Bab al-Mandeb strait from government-aligned forces backed by Saudi Arabia this week, raising fears that the Iran-armed faction is now better positioned to close the southern end of the Red Sea to commercial shipping should its leaders choose to do so.

The Houthis’ capture of Mokha and Perim Island, just north of the strait, gives the rebels a geographic advantage from which they could more easily fire precision missiles into the waterway. This would likely impose further strain on the flow of oil exports from Arab countries in the Gulf, potentially adding to the economic pressure caused by Iran’s ongoing attacks on commercial shipping in the Strait of Hormuz.

Abdullah al-Saadi, the Yemeni government’s envoy to the UN, accused the Houthis of “attempting to impose a new reality in the Red Sea” during an emergency meeting of the Security Council on Thursday. “We are defending Bab al-Mandeb as a matter of international and regional security,” al-Saadi told the Security Council.

But Washington appeared uninterested in getting directly involved in the conflict in the immediate aftermath of the Houthis’ breakout.