A series of vessels came under fire in the wider Gulf region amid ongoing exchanges of strikes between the US and Iran, including a vessel hit off Iraq, a British maritime monitor said on Wednesday.

Tehran said it attacked 20 ships trying to pass through the Strait of Hormuz during a latest round of salvoes that came with the six-month Middle East war deadlocked.

Iran has maintained its stranglehold on the strategic Strait of Hormuz as Washington continues pressing its counterblockade of Iranian ports.

The United Kingdom Maritime Trade Operations (UKMTO) said it had received a report of a tanker being struck 28 nautical miles southeast of the Iraqi port city of Al-Faw.

Iraq’s transport ministry said at 5:30 am local time (0230 GMT), a Panama-flagged tanker carrying fuel oil was struck by an "unknown source" in Iraqi territorial waters, causing material damage to the vessel's hull.

Earlier the UKMTO said "several merchant vessels in the Northern Arabian Gulf and the Gulf of Oman" were "subject to disabling fire as part of ongoing military activity in the region".

It also reported a vessel 24 nautical miles northwest of Port Rashid, in the UAE, that it said was listing, potentially due to an attack.

"The Master of a tanker has reported sighting a vessel listing while at anchor, possibly indicating water ingress following an attack from an unknown projectile," it said.

Iraq's transport ministry said at 5:30 am local time (0230 GMT), a Panama-flagged tanker carrying fuel oil was struck by an "unknown source" in Iraqi territorial waters, causing material damage to the vessel's hull.

On Wednesday, Iran's Revolutionary Guards said they attacked two US vessels, eight oil tankers and 10 "non-compliant vessels" trying to pass through the Strait of Hormuz, state media reported.

The attacks followed US strikes on Iranian vessels, with Tehran also threatening to attack oil tankers off Kuwait and Bahrain.