A British man has been killed in Ukraine and a second Briton is missing.
Scott Sibley, believed to be 36, has been named as the Briton who died.
It is thought the pair could have been fighting against Russian troops as volunteers in support of Ukraine‘s military, although this has not been confirmed.
British nationals, and other foreigners, have also travelled to Ukraine to take part in humanitarian assistance.
Mr Sibley is a veteran of the British armed forces, it is understood.
The Foreign, Commonwealth and Development Office (FCDO) did not provide any details on what the men had been doing in Ukraine.
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An FCDO spokesperson said: “We can confirm that a British national has been killed in Ukraine and are supporting their family.”
On the second British man, the FCDO spokesperson said: “We are aware of a British national who is missing in Ukraine and are supporting their family. We are urgently seeking further information.”
The Foreign Office did not provide details on when the British national was killed and when the other man went missing and is urgently seeking further information.
There are a number of fighters who have decided to head to Ukraine to join the fight against Vladimir Putin’s forces, including British veterans.
At the beginning of the war, Ukraine’s government urged volunteers from across the world to come and help support its armed forces as they took on Russia’s invasion.
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The advice from the UK government has been that people should not travel to Ukraine to fight, but they can support Ukraine in many other ways.
A number of individuals decided to come anyway and are in the country helping Ukraine’s military defence.
It comes over a week after two British fighters – Shaun Pinner and Aiden Aslin – were captured by Moscow’s forces.
The pair, who have been held in Ukraine, appeared on Russian state TV and asked to be swapped for Viktor Medvedchuk, a Ukrainian politician who is close to Vladimir Putin.
But asked by Sky News’ Kay Burley about the potential for such a swap, Northern Ireland Secretary Brandon Lewis said: “We’re actually going through the process of sanctioning people who are close to the Putin regime.
“We’re not going to be looking at how we can help Russia, we’re looking to actually ensure that the Putin regime is unsuccessful in this abhorrent invasion and we’ll continue to do everything we can to support the Ukrainian people and the Ukrainian president and government to defeat Putin.”