US President Donald Trump on Friday blamed Iran for carrying out a drone strike on a cargo ship in the Strait of Hormuz, calling it a “foolish violation” of the ceasefire agreement with the US.

One drone damaged the upper deck of the ship but the ship was able to proceed, Trump said. The US shot down three other drones aimed at the ship, he said.

His post on social media did not identify the ship or the time of the strike, but on Thursday the British military said a vessel was hit by a projectile off the coast of Oman.

The development comes during a fragile time for the US and Iran as they work to negotiate a permanent end to the war. Iran has increasingly challenged the region and the US over its control of the Strait of Hormuz, even with the current interim deal it reached with the US last week.

A missile warning in the United Arab Emirates caused by a technical glitch earlier on Friday underscored the ongoing tensions in the region, following the attack on the cargo vessel and Israeli strikes in Lebanon over the past few days.

The mobile phone alert startled many across the city state of Dubai, the first such alert since the interim ceasefire.