US President Donald Trump announced on Sunday that the US Navy had fired on and then taken control of the Touska cargo ship in the Sea of Oman.

Trump says the Iran-flagged vessel is subject to US sanctions.

"Such conduct bears the hallmarks of piracy in nature and amounts to a dangerous escalation that severely endangers the safety and security of vital shipping lanes," Amir Saeid Iravani, Iran's Ambassador to the United Nations, said Tuesday in a letter addressed to the Security Council and the Secretary-General.

"Moreover, this unlawful act constitutes a clear and material breach of the ceasefire of 8 April 2026 and qualifies as an act of aggression," under the terms of the UN charter, he added.

Iravani urged the UN to condemn the seizure and demand the ship's release.

Trump wrote on his Truth Social platform Tuesday that he was extending the ceasefire with Iran to allow more time for negotiations, but would maintain a US naval blockade of the country's ports.

Trump said Sunday that the Touska was seized after failing to respond to a warning to stop.

"The Iranian crew refused to listen, so our Navy ship stopped them right in their tracks by blowing a hole in the engineroom," the president added.