Iranian-backed forces are believed to have seized an oil tanker off the coast of the United Arab Emirates, three maritime security sources said.
It comes after Britain's maritime trade agency reported a "potential hijack" in the area today.
Two of the sources identified the vessel as the Panama-flagged asphalt tanker Asphalt Princess in an area in the Arabian Sea leading to the Strait of Hormuz, the conduit for about a fifth of the world's seaborne oil exports.
The US State Department said it was aware of reports of a maritime incident in Gulf of Oman and is "concerned" and looking into it.
Britain's foreign ministry is "urgently investigating" an incident on a vessel off the UAE coast, a spokesperson said.
Iran's Foreign Ministry had earlier said reports of security incidents involving several ships near the UAE coast were "suspicious", and it warned of any effort to create a "false atmosphere" against the Islamic Republic.
Tensions have simmered in the region after an attack last week on an Israeli-managed tanker off the Omani coast killed two crew members and was blamed on Iran by the United States, Israel and Britain.
The deaths occurred following an apparent drone attack on the Japanese-owned, Liberian-flagged oil tanker, MT Mercer Street.
Washington has called for a collective response against Tehran over the incident. The Iranian authorities have denied any involvement.
The Bahrain-based US Navy's Fifth Fleet and UAE authorities did not immediately reply to a Reuters request for comment about the incident.
The UK Maritime Trade Operations, in a warning notice based on a third party source, had earlier reported a "potential hijack" and advised ships to exercise extreme caution due to the incident around 60 nautical miles east of the UAE's Fujairah emirate.
The Times of London newspaper also reported that the Asphalt Princess had been hijacked, citing British sources as saying they were "working on the assumption Iranian military or proxies boarded the vessel".
Iranian foreign ministry spokesman Saeed Khatibzadeh said that "reported 'incidents' in the Persian Gulf and broader region appear utterly suspicious", in a message on Twitter.
"Reaffirming our strong commitment to regional stability and maritime security, Iran stands ready to offer assistance in case of any maritime accidents," Mr Khatibzadeh added.
Earlier today, at least five ships in the sea between the UAE and Iran updated their AIS tracking status to "Not Under Command", according to Refinitiv ship tracking data.
Such a status generally indicates a ship is unable to manoeuvre due to exceptional circumstances.
Reuters could not confirm this Refinitiv data had any connection to the reported incident.