Reports are coming in of an incident between Russian Special Forces and the Ukrainian Navy.
According to the BBC, a tugboat was seized and at least two Ukrainian Sailors have been injured.
It said two gunboats and a tug were captured by Russian special forces after a chase. Two Ukrainian crew members were injured.
Russia is yet to comment on the claims.
It earlier accused Ukraine of illegally entering Russian waters, blocking access to the Sea of Azov with a tanker put under a bridge in the Kerch Strait.
Ukrainian President Petro Poroshenko called an urgent meeting of his “war cabinet”, his spokesperson said.
The US is said to be holding ‘Emergency Talks’ to discuss the incident.