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, the US president 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 US and Iran are still negotiating terms of the interim peace deal, including issues such as getting ships through the key strait and addressing the future of Iran’s stockpile of highly enriched uranium. Under the interim deal, the two sides have 60 days to work out the details.