Iran accused the United States of breaching their ceasefire Tuesday (May 26) and warned it was ready to retaliate after overnight US strikes targeting Iranian missile sites and mine-laying boats threatened a deal to end the war.

The Brent benchmark oil price jumped up by more than 4 per cent after US Central Command announced the new wave of bombings, and China urged both sides to respect the truce and to resolve their dispute peacefully.

According to the maritime safety monitor UKMTO, a blast damaged a tanker on the waterline off Oman - although the crew and vessel were reportedly safe after what was described as an "external explosion".

Iranian state media reported overnight blasts in the southern port city of Bandar Abbas, near the Strait of Hormuz, and the country's Revolutionary Guards said its forces had downed a US drone entering its airspace and had fired at an F-35 fighter jet.

"The US terrorist army, continuing its illegal and unjustified actions since the ceasefire ... has, in the past 48 hours, committed a gross violation of the ceasefire in the Hormozgan region," the Iranian foreign ministry said.

It added that Tehran "will not leave any evil unanswered and will not hesitate to defend the Iranian nation", without elaborating.

In a statement marking the start of the Eid al-Adha holiday, Tehran's supreme leader Ayatollah Mojtaba Khamenei declared that Washington was losing its influence in the Middle East and warned countries in the region to stop hosting bases from which the US could launch attacks.

The United States, he said in a written statement, "in addition to no longer having any safe haven in the region for aggression and the establishment of military bases, is moving further and further away from its former position with each passing day".

Tim Hawkins, a spokesman for US Central Command, said: "US forces conducted self-defence strikes in southern Iran today to protect our troops from threats posed by Iranian forces."