A Royal Navy ship which has been sent to Ukraine will send a strong message to Russian President Vladimir Putin, the UK's defence secretary says.
HMS Echo was sent into the Black Sea earlier this month, after Russia seized three ships belonging to Ukraine's navy and their crews.
Defence Secretary Gavin Williamson has visited the ship in the port of Odessa.
He said the presence of the British ship shows support for Ukraine in the face of increased Russian aggression.
It will be followed by other Royal Navy ships as part of a more constant British presence, he said.
Nato has recently stepped up its operations in the Black Sea with increased warship patrols.
There are increasing tensions between Russia and Ukraine over access to the area off the coast of Crimea.
Russian forces seized control of Ukraine's Crimean peninsula in March 2014, in a move condemned internationally.
Mr Williamson paid a pre-Christmas visit to HMS Echo soon after it docked in Odessa on Friday.
He said the ship was there to send a message to President Putin that Britain stands in solidarity with Ukraine.
"What we are saying to Russia, what we are saying to President Putin - they cannot continue to act with no regard or care for international laws or international norms," he said.
The defence secretary made a point of meeting the families of the 24 Ukrainian sailors who are still being held and are now awaiting trial in Moscow.
HMS Echo is not expected to sail through the Kerch Strait near Crimea - close to where the Russian Navy rammed, shot at and seized the three Ukrainian Navy vessels in November.
Moscow has described the Royal Navy vessel - which is used to collect data about the ocean - as a spy ship.