The United Kingdom is not looking to help Moscow with the prospect of a prisoner swap that would trade pro-Russian oligarch and Ukrainian politician Viktor Medvedchuk for two British fighters captured in Ukraine by Russian forces, a government minister said Tuesday.

Northern Ireland Secretary Brandon Lewis would not confirm to Sky News if his government is working to return the fighters to the UK, saying he would not comment on “what are effectively national security issues.”

Video footage of both captive Britons has aired on Russian TV. They previously fought with the UK armed forces and were volunteering with the Ukrainian military in the fight against Russia.

“They shouldn’t have been there, it is an illegal act to be there,” Lewis said.

Asked about the prospect of exchanging the Britons for Medvedchuk, who is currently detained by Ukrainian forces, he said: “We’re actually going through the process of sanctioning people who are close to the [Russian President Vladimir] Putin regime. We’re not going to be looking at how we can help Russia.”

“We always have a responsibility for British citizens which we take seriously,” he said. “We’ve got to get the balance right with Ukraine, that’s why I say to anybody, do not travel illegally to Ukraine. The armed forces of Ukraine have the support of the UK. We’re continuing to put that support in and that’s the right way to do it.”

Lewis encouraged people who want to help Ukraine to do so through the “right channels” — such as financially or by opening their homes to refugees — “rather than taking very dangerous and actually not legal processes to go out” and fight, he said.

Medvedchuk served as a go-between for Moscow and Kyiv after the outbreak of the Donbas conflict in 2014 by leveraging his personal ties with Putin. In a 2019 interview with filmmaker Oliver Stone, Putin acknowledged that he was godfather to Medvedchuk’s daughter.

“I would not say that we are very close but we know each other well,” Putin said. “He was [former Ukrainian] President [Leonid] Kuchma’s chief of staff, and it was in this capacity at the time that he asked me to take part in the christening of his daughter. According to Russian Orthodox tradition, you can’t refuse such a request.”

Ukrainian President Volodymyr Zelensky announced last week that Medvedchuk had been detained in a “special operation.” Medvedchuk’s wife, Oksana Marchenko, has posted videos appealing for the release of her husband in exchange for British nationals taken captive.