The UK's Maritime Trade Operations (UKMTO) reported a boat colliding with a ship in the Arabian Gulf about 150km north-west of Jebel Ali in the Arabian Gulf on Sunday.
It said a small craft struck a vessel and began trying to hit other ships in the area, before its crew transferred on to another small boat. The report was posted by UKMTO at 4.15pm.
"Merchant vessel remained on scene for some time before proceeding to next port of call," UKMTO's report said, referring to its own ship.
It said the merchant vessel then received a barrage of messages from a group claiming to be local authorities, requesting the crew to stop and enable representatives of the claimed authority to board the UKMTO's ship. All crew are safe and well.
The incident has not been confirmed by UAE authorities.
"Vessels are advised to transit with caution and report any suspicious activity to UKMTO," a statement said.
VHF radios allow communication between boats, marinas and coastguards.
