A British monitoring agency and maritime security firm Ambrey said on Tuesday that they had received reports that a vessel had been boarded off Somalia by multiple people who were now in control of it.

The United Kingdom Maritime Trade Operations (UKMTO) agency said the boarding incident happened 600 nautical miles east of Somalia's capital Mogadishu.

"Unauthorised persons now have control of the vessel," UKMTO said in a statement, adding that the people had boarded the vessel from one small and one large craft.

Ambrey said the incident off Somalia involved 20 armed people boarding a Bangladesh-flagged bulk carrier.

The carrier was sailing to Hamriya, United Arab Emirates, from Maputo, Mozambique, Ambrey said.

"The crew were reported in the citadel, however, this is assessed as unlikely. There have been conflicting reports regarding the crew's whereabouts," Ambrey said in a statement.

If the incident is confirmed as a pirate attack it could fuel concerns about a resurgence of Somali piracy in the Indian Ocean.

Maritime security sources said in December that according to their assessment an attack that month was the first hijacking of a merchant ship by Somali pirates since 2017.

Pirates who caused chaos in key waterways from 2008 to 2018 may have returned, the sources said, possibly encouraged by a relaxation of security, or taking advantage of the chaos caused by attacks on shipping by Yemen's Iran-aligned Houthi group amid the war in Gaza.