The RAF has scrambled a squadron of Typhoon fighter jets to the Ukraine border.
The Ministry of Defence confirmed jets are being sent from RAF Coningsby in Lincolnshire to Romania as part of a "long-standing NATO mission" over the Black Sea region.
Announcing the drill on Twitter, the MoD said: "The UK is committed to #NATO and European security".
The agency said the four jets, part of the 3 (Fighter) Squadron, are being deployed to the Mihail Kogalniceanu Air Base on the Romanian Black Sea coast.
A 150-strong team of RAF personnel are supporting the operation from RAF Wittering in Peterborough, the Daily Star reports.
James Heappey, Minister for the Armed Forces, said: “The UK remains committed to NATO and European security in the face of Russian aggression and the unprovoked invasion of Ukraine.
“Operation Biloxi is a long-standing NATO mission and the Royal Air Force are playing a central role in security and deterrence in Europe.”
Operation Biloxi is the British name for the NATO Air Policing mission, with this occasion marking the fourth time since 2017 the RAF has conducted it, the Express reports.
Air Vice-Marshal Phil Robinson, Officer Commanding 11 Group also said: “The arrival of our personnel and equipment in the region highlights the RAF’s continued commitment and contribution to the NATO Air Policing mission in Romania.
“During the deployment, we will be working alongside our Romanian and other NATO partners, enabling the delivery of the mission and protecting and reassuring our allies, whilst building confidence and maintaining deterrence.”
According to ArmedForces.co.uk, the latest estimated cost of the RAF Typhoon programme was some £17.6 billion, making it the most expensive weapon system yet produced for the UK Armed Forces.
A rough unit cost estimate is £110 million (demonstration and manufacture divided by 160 aircraft).
Meanwhile, the MoD said in their latest intelligence update about the invasion of Ukraine that Russia is continuing to bombard major cities.
They said: “Russia continues to besiege a number of major Ukrainian cities including Kharkiv, Chernihiv and Mariupol.
“Russian forces are proving reluctant to engage in large scale urban infantry operations, rather preferring to rely on the indiscriminate use of air and artillery bombardments in an attempt to demoralise defending forces.
“It is likely Russia will continue to use its heavy firepower on urban areas as it looks to limit its own already considerable losses, at the cost of further civilian casualties.”
It comes as the UK also announced it will send £2 million worth of vital supplies to Ukrainian cities surrounded by Russian troops as the conflict continues.
Foreign Secretary Liz Truss has confirmed the UK will send a donation of dried food, tinned goods and water to Ukraine following a request from the country's government.
Warehouses in Poland and Slovakia are being readied to supply the goods from early next week, the Foreign, Commonwealth and Development Office (FCDO) said.
From there, around 25 truckloads will then be transported by road and rail to the Ukrainian communities in the greatest need.
Ms Truss said teams are "working day and night" to help get humanitarian assistance to those requiring it.
