U.S. President Donald Trump said on Monday he would hold Iran responsible for any attacks carried out by the Houthi group that it backs in Yemen, as his administration expanded the biggest U.S. military operation in the Middle East since Trump returned to the White House.

President Trump declared Monday that he would consider every shot fired from the Houthis to be an attack from Iran and threatened to hold the regime in Tehran responsible.

The U.S. president’s threat raises questions about whether he would risk a wider Mideast war over disruptions to global commerce.