Armed men in "military-style" uniforms boarded an oil tanker in the Gulf of Oman on Thursday, a maritime risk management company said, the latest in a spate of shipping incidents in the region.

The Marshall Islands-flagged St Nikolas was boarded at about 7:30 am (0330 GMT) 50 nautical miles east of Sohar in Oman and then headed towards Bandar-e-Jask in Iran, according to British firm Ambrey.

"The individuals covered the vessel's cameras," Ambrey reported, adding that a security officer "reported hearing unknown voices over the phone along with the master's voice".

"The armed suspects are reportedly wearing 'military-style black uniforms with black masks,'" it added. 

The incident was also reported by United Kingdom Maritime Trade Operations, a British maritime security agency.

The St Nikolas was sailing from the Iraqi port of Basra to Turkey, according to Marine Traffic, a tracking website.

Ambrey said the recently renamed tanker was previously prosecuted and fined for carrying sanctioned Iranian oil, which was confiscated by US authorities.

"Iran has previously taken action against those it has accused of cooperating with the US," it added.

The Gulf of Oman, a key route for the oil industry that separates Oman and Iran, has witnessed a series of hijackings and attacks over the years, often involving Iran.

Shipping in the resource-rich region is also on heightened alert following weeks of drone and missile attacks by Yemen's Huthi rebels in the Red Sea.