A ceasefire between Iran and the United States was teetering Monday as the two countries traded fire over the strategic Strait of Hormuz and the United Arab Emirates reported attacks for the first time since the truce was declared nearly a month ago.

A day after President Donald Trump announced an operation to escort trapped vessels through the strait, Fox News quoted him as threatening that Iran would be “blown off the face of the earth” if it attacks US ships.

Iran appeared undaunted as it vowed to keep exerting control over the Strait of Hormuz, the narrow waterway through which one-fifth of the world’s oil flowed before the United States and Israel attacked Iran on 28 February.