The Iran-backed Houthi movement in Yemen has announced a blockade of Saudi Arabia in the Red Sea, a move that could potentially open a new front in the war in the Middle East, The New York Times writes.

Until now, Yemen’s Houthis had stayed out of the U.S. war with Iran. That changed on Monday, when the Iran-backed Houthi militia, which controls a significant part of Yemen, announced a naval blockade of Saudi Arabia, a U.S. ally.

This move threatens to open a new front in the regional war and further disrupt global energy supplies.