Two British nationals are currently being held by Russian forces as the 'battle for Donbas' has begun.
Aiden Aslin, 28, and Shaun Pinner, 48, were both captured within days of each other while fighting alongside Ukrainian forces in the besieged city of Mariupol.
Both men appear to have been paraded on Russian state TV speaking about their captures.
Mr Aslin and Mr Pinner are both still being held as their families plead with the Russian military to see them as prisoners of war as opposed to mercenaries.
Vladimir Putin 's war machine has commenced its bombardment of eastern Ukraine with chilling footage posted on social media showing the night sky lit up amid the relentless fresh shelling of cities.
Kremlin forces launched their long-anticipated offensive through the east of Ukraine in what is being seen as the second phase of the conflict, beginning on Monday night.
Footage on social media appears to show repeated heavy shelling centred in the regions of Donetsk and Luhansk while Ukrainian media reported some powerful explosions in the cities of Marinka, Slavyansk and Kramatorsk.
Here's everything we know about Mr Aslin and Mr Pinner.
Who is Aiden Aslin?
Mr Aslin is a 28-year-old from Newark, Nottingham, who was already living in Ukraine when the war broke out.
In 2018, he joined Ukraine's armed forces as a marine and has since applied for citizenship there.
Before the war broke out, he was living in Ukraine with his fiancée and was building a house and a life there.
He previously fought alongside the Kurdish YPG against Isis in Syria in 2015 and 2016.
The former care worker has dual citizenship.
What has his family said?
His mum Angela Wood recently told Sky News her son should be treated as a legitimate prisoner of war because he's a Ukrainian marine.
It comes after Russian media suggested he was a mercenary - or a soldier for hire.
She said: "They have put him on their TV... he is alive, but they are now accountable.
"He's not a mercenary, he's not a volunteer, he did not go out there in the last month and think 'I'm going to fight, I'm going to get glory'.
"He has been out there four years and he is a legitimate Ukrainian marine."
She added: "Aiden's fiancée is Ukrainian and his life is there.
"He's a proud Ukrainian citizen, so seeing him called a mercenary is hurtful."
What has he said on TV?
Last week, the Kremlin state broadcasted footage of the Brit with a gash on his forehead, sparking concerns about his treatment in captivity.
The Brit was forcibly interviewed by a Russian journalist who asked him various questions about his time in Ukraine.
The interviewer asked him "Tell me, did you kill people?", with Aiden replying "I don't know".
He then added: "I didn't do any fighting."
When asked if he saw how people were killed, Aiden looked off camera before answering 'no'.
Who is Shaun Pinner?
Mr Pinner is a 48-year-old from Bedfordshire and a former Royal Anglian soldier.
The Brit moved to Ukraine four years ago before joining the Ukrainian marines in hopes of passing over the expertise he picked up while in the British Army.
His family say he was due to complete his three-year contract in the military by the end of 2022 with future plans to move to a humanitarian role within Ukraine.
What has he said on TV?
During a video shown on Russian TV channel, he said: “Hi, I’m Shaun Pinner. I am a citizen of the UK.
"I was captured in Mariupol. I am part of the 36 Brigade First Battalion Ukrainian Marines.
“I was fighting in Mariupol for five to six weeks and now I’m in Donetsk People’s Republic.”
When asked if he wished to address the British Government and speak directly to Boris Johnson, Mr Pinner added: “Yes, I’d like to appeal to the Government to send me back home. I’d love to see my wife again.
"Mr Boris Johnson. Obviously I’m Shaun Pinner.
"A lot’s gone on over the last five or six weeks that I’m not fully aware of.
"Obviously I understand that Mr Medvedchuk has been detained and we look to exchange myself and Aiden Aslin for Mr Medvedchuk.
“Obviously I would really appreciate your help in this matter and pushing this agenda.
"Myself, I’ve been treated well. Fully understand the situation that I’m in.
"We’ve been fed, watered, and that’s all I can really say, but I beg on my behalf and Aiden Aslin’s behalf for help us in an exchange for Mr Medvedchuk.”
What has his family said?
His family has issued a plea of their own for Mr Pinner to be treated as a prisoner of war as he is a serving Ukrainian soldier.
In a statement released by the Foreign, Commonwealth & Development Office (FCDO) on behalf of Mr Pinner’s family, they go into more detail on how he recognises Ukraine as “his adopted country”.
They said: “Shaun was a well-respected soldier within the British Army serving in the Royal Anglian Regiment for many years.
"He served in many tours including Northern Ireland and with the United Nations in Bosnia.
“He progressed into the Ukrainian Marines as a proud member of his unit.
"At the end of 2022, his three-year contract is due to end and he was planning to enter a humanitarian role within Ukraine.
“Our family is working with the Foreign Office along with the family of Aiden Aslin to ensure their rights as prisoners of war are upheld according to the Geneva Convention."
They added: "Shaun is a funny, much-loved, well-intentioned husband, son, father, brother and friend to many.
“Our hearts go out to all those caught up in this horrific conflict.”
What has the Foreign Office/British Government said about the captured British soldiers?
A Foreign Office source said it was aware of the detention of two British nationals and had been in touch with their families to support them, adding that it was advising against all travel to Ukraine.
The Foreign Office called on the Kremlin to treat prisoners humanely.
A source from the department condemned "the exploitation of prisoners of war for political purposes".
Who is Mr Medvedchuk?
Viktor Medvedchuk is a close friend of Putin, who is godfather to his daughter.
The pro-Russian Ukrainian politician Mr Medvedchuk appealed in a video released by Ukraine's security service on Monday to be handed over to Moscow in a prisoner swap for Ukrainian forces and civilians trapped in the besieged city of Mariupol.
He led the most prominent pro-Russian political coalition, Opposition Platform – For Life until he was arrested and charged with treason in May 2021.
The charges he faces relate to alleged sale of military secrets to Russia and exploitation of the natural resources of occupied Crimea.
Mr Medvedchuk denies the charges and maintains the arrest was politically motivated.
He was under house arrest in Ukraine when Russia invaded on February 24, but escaped and disappeared soon afterwards.
He was recaptured by Ukraine’s security service on April 12 and Ukranian President Volodymr Zelensky immediately suggested exchanging him for Ukrainian prisoners.
