President Donald Trump vowed that Iran “will pay” for killing three U.S. soldiers in recent days, even as mediators proposed a new truce with the Middle East war widening further.

“Every time Iran kills an American Soldier they will pay for that killing many times over!” Trump wrote on social media on Monday.

Earlier, Iran said mediators were in touch with proposals on how to ease hostilities after more than a week of worsening clashes. Tensions remain high and the conflict looked set to expand further after Tehran-backed Houthi militants in Yemen threatened to blockade Saudi Arabia in the Red Sea.