A Moscow court in April jailed 42-year-old Kara-Murza for 25 years, the harshest sentence of its kind since Russia invaded Ukraine. He was convicted of treason and other offences in a trial he said was politically motivated.

US officials have condemned his detention as politically motivated and called for his release, but a formal designation of wrongful detention would mobilise US government resources and involve the presidential envoy for hostage affairs in the case.

The Helsinki Commission, an agency that includes members of the US House and Senate, on Wednesday heard evidence from Kara-Murza’s wife and daughter.

Republican congressman Joe Wilson, who chairs the commission, said a wrongful detention determination “would energise efforts to bring Vladimir home,” but said calls from lawmakers for the State Department to issue one have so far gone unanswered.

“We’ve not received a clear response as to why they’ve failed to act with a…sense of urgency,” said Wilson.

Wilson said he was introducing the Vladimir Kara-Murza Action and Freedom Act, a bill with bipartisan support that would require the State Department to issue a wrongful detention determination within 30 days or provide a rationale for not doing so.

The State Department did not immediately respond to a request for comment.

Vladimir’s wife, Evgenia Kara-Murza, told the commission a nerve condition her husband developed after two past poisonings, which she says were carried out by Russian agents, has worsened since his detention.

Russian authorities have denied involvement in the incidents.

“Today, Vladimir is somewhere in Siberia, about 2,000 miles away from Moscow, with no contact with his lawyers, let alone his family members,” she said.