The wife of one of Russian President Vladimir Putin’s most prominent critics says her husband has again been poisoned.

Vladimir Kara-Murza was hospitalized last week with sudden organ failure and is on life support in a medically induced coma, according to his wife, Yevgenia. On Tuesday, she said doctors have diagnosed him with an “acute poisoning by an unidentified substance,” according to the The Associated Press.

In 2015, Vladimir Kara-Murza almost died as a result of sudden kidney failure. Then, he said he had been poisoned. French laboratories could not determine a specific poison but found high levels of heavy metal in his blood at the time, according to The New York Times.

Kara-Murza was a close associate to prominent opposition leader Boris Nemtsov, who was murdered in 2015. He is a journalist and involved in the pro-democracy group Open Russia.

Members of Congress in the United States from both parties have called on President Trump and his administration to speak out on his recent hospitalization.

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"We do not know the details on the cause for this most recent health issue, but it appears to be part of an alarming trend where Russian political opposition are targeted for their work," Sen. Ben Cardin Benjamin (Ben) Louis CardinPPP application window closes after coronavirus talks deadlock Congress eyes tighter restrictions on next round of small business help Senate passes extension of application deadline for PPP small-business loans MORE (D-Md.) said last week.

Sen. Marco Rubio Marco Antonio RubioHillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Intelligence chief says Congress will get some in-person election security briefings Republican Senators raise concerns over Oracle-TikTok deal MORE (R-Fla.), however, pointed to Putin.

“Vladimir Putin does not deserve any benefit of the doubt here, given how commonplace political assassinations and poisonings have become under his regime," he said in a statement last week.

Bipartisan members of Congress slammed Trump over the weekend for defending Putin in an interview with Fox News's Bill O'Reilly. When O'Reilly called Putin a "killer," Trump responded by saying the U.S. also has "a lot of killers."

"There are a lot of killers. We've got a lot of killers. What, you think our country is so innocent?" Trump said.