Somali Maritime Forces and pirates are involved in fighting aboard a hijacked oil tanker The Aris 13 reports suggest.
The stricken ship is anchored off the Somali coast near the town of Alula.
There have been no reports of hijacking in the area for five years but the Aris 13 appears to have taken a shorter route than planned, leaving it vulnerable to attack.
The pirates apparently boarded the slow moving and unprotected ship before taking control of the vessel. The crew are thought to be held
in a locked room.
Officials have ridiculed statements made by the pirates, who claim to have killed at least one member of the maritime forces.
The notorious Somalian pirates rose to infamy between 2005 and 2011, even holding Asian hostages for five years but more recently patrols have secured the shipping routes and things have been relatively quiet.