Iran has denied involvement in an attack on an oil tanker which killed two people, including a British security guard, off the coast of Oman.
It comes as Israel alleges that Tehran carried out the assault amid heightened regional tension.
The Ministry of Defence (MOD) is investigating the incident, which US Navy explosives experts believe involved a drone strike.
On Sunday, Iranian Foreign Ministry spokesman Saeed Khatibzadeh described the allegation Iran carried out the attack as "baseless".
"Such blame games are nothing new," Mr Khatibzadeh said. "Those who are responsible for this (attack) are the ones who made it possible for the Israeli regime to set its foot in this region."
He added: "This is not strange, the well-known anti-Iran lobby in the US uses any opportunity to make… accusations against the Islamic Republic of Iran."
Thursday's strike on the ship, MV Mercer Street, is thought to be the first fatal attack after years of assaults on commercial shipping in the region linked to tension with Iran over its tattered nuclear deal.
The vessel is managed by London-based Zodiac Maritime – part of Israeli billionaire Eyal Ofer's Zodiac Group.
The firm said two crew members – one British and one Romanian – were killed but believes no other crew members were harmed.
UK maritime security group Ambrey said one of its team members was killed on board the ship.
The MV Mercer Street, empty of cargo, had been on its way from Dar es Salaam in Tanzania to Fujairah in the United Arab Emirates when it was hit, Zodiac Maritime said.
It was north-east of the Omani island of Masirah, 185 miles south-east of Oman's capital Muscat.
Oman's state-run news agency described the area as "beyond Omani regional waters" and said its forces responded to the tanker's mayday call.
The attack, which Iran denies launching, comes when the country appears ready to toughen its stance on the west, preparing a new hard-line president and protégé of Supreme Leader Ayatollah Ali Khamenei.
The stricken ship was escorted by US aircraft carrier USS Ronald Reagan and destroyer USS Mitscher to safe port, according to the US Navy's 5th fleet based in the Middle East.
It said: "US Navy explosives experts are aboard to ensure there is no additional danger to the crew and are prepared to support an investigation into the attack.
"Initial indications clearly point to a (drone)-style attack."
An MOD spokesperson said: "We are aware of reports of an attack on a merchant vessel off the coast of Oman. UK military headquarters in the region are currently conducting investigations."
Cover image: A library picture of MVMercer Street (Picture: Alamy).