WASHINGTON -- The wife of a prominent Russian opposition activist who mysteriously fell ill in Moscow this week is seeking his evacuation to Europe or Israel for toxicology tests, saying his condition has not improved.

Vladimir Kara-Murza Jr., a former political ally of slain Russian opposition leader Boris Nemtsov, lost consciousness in Moscow on May 26 and was hospitalized with what his wife calls "symptoms of poisoning."

"His condition has not improved since; he has not regained consciousness," his wife, Yevgenia, said in an e-mail to RFE/RL and other media outlets.

She said the hemodialysis he underwent to treat kidney failure "has not had any effect" and asked that he be evacuated by plane from Russia "to a medical center in Europe or Israel where full toxicology testing and treatment can be done."

But Aleksei Svet, head doctor at Moscow's Pirogov 1st City Hospital where Kara-Murza is a patient, told Interfax on May 29 that it was not possible to transport him.

"We are responsible for the patient," Svet said. "The patient is not transportable."

Svet had said earlier that Kara-Murza was "most likely" suffering from a "severe bout of pancreatitis and, possibly, double-sided pneumonia."

Kara-Murza’s father, who is also named Vladimir, told RFE/RL's Russian Service on May 28 that "the situation appears to be more serious than we thought."

"His kidneys stopped working in the evening. And Volodya [Vladimir Kara-Murza Jr.] is alive now thanks to an artificial kidney, thanks to hemodialysis, which can lead to lesions of other organs," Vladimir Sr. added. "His lungs are being artificially ventilated. He is connected to 10 devices."

Kara-Murza's father is a journalist with RFE/RL’s Russian Service.

The activist's family has been cautious publicly about whether foul play may have been involved, stressing that so far there is no evidence pointing to such a scenario.

"There is no criminal case so far, none has been opened because he is simply a normal patient who arrived at a Moscow hospital by ambulance. That’s his status, nothing more," his father told the Moscow-based Ekho Moskvy radio on May 28.

The elder Kara-Murza said Russian doctors believe his son may have ingested a dangerous amount of antidepressants that he may have begun taking after Nemtsov’s murder three months ago.

"Our task right now is to bring him to a normal trajectory of recuperation," he told Ekho Moskvy. "We’ll establish the cause [of the illness] later."

Kara-Murza, 33, serves as a coordinator for Open Russia, a nongovernmental organization founded by former oil tycoon Mikhail Khodorkovsky, a prominent critic of President Vladimir Putin who spent over a decade in prison in Russia and now lives in Switzerland.

He fell ill one day after the group released a documentary film accusing the government of Russia's republic of Chechnya of corruption and human rights abuses under the region's strongman leader, Kremlin ally Ramzan Kadyrov.

A U.S. congressional source told RFE/RL that U.S. and British diplomats in Moscow were coordinating to possibly have Kara-Murza, a dual Russian-British citizen, medically evacuated from Russia.

Will Stevens, a spokesman for the U.S. Embassy in Moscow, referred a request for comment to the British Embassy.

A spokesman for the British Foreign Office told RFE/RL that British diplomats "are providing consular assistance to a dual British national taken ill in Moscow."

A British Foreign Office source said that medical evacuation was not a service included in consular support. "We would advise people to follow the advice of medical professionals," the source told RFE/RL.

The source declined to discuss Kara-Murza's case but said that, in general, consular assistance "usually would include talking to the family of the person involved and local authorities," as well as hospital visits.

Kara-Murza's father told RFE/RL's Russian Service that he did not rule out his son's possible medical evacuation from Russia.

Kara-Murza has been based in Washington for many years but has traveled frequently to Russia to conduct grassroots political work for a range of liberal opposition groups.

He is a senior member of the opposition RPR-Parnas party, which was co-founded by Nemtsov, a former Russian deputy prime minister and vocal Kremlin critic who was shot dead in central Moscow on February 27.

During his time in the U.S. capital, where his wife and children reside, Kara-Murza has served as a key liaison between Russian opposition groups and top American policymakers.

Last month he joined former Russian prime minister and current Kremlin opponent Mikhail Kasyanov to lobby U.S. lawmakers to impose sanctions on Russian television "propagandists" they accuse of spearheading a media vilification campaign that they say helped lead to Nemtsov's slaying.

"I am deeply concerned about the mysterious illness of Vladimir Kara-Murza, especially given the recent murder of Boris Nemtsov and the number of Putin's opponents who have been poisoned," U.S. Representative Chris Smith (Republican-New Jersey), said in a statement to RFE/RL.

"I strongly urge the Russian government to guarantee Mr. Kara-Murza's safety and facilitate his transfer to a hospital outside of the Russian Federation for further evaluation and care," added Smith, the chairman of the U.S. Helsinki Commission.

U.S. Senator Benjamin Cardin (Democrat, Maryland) said in a May 28 tweet that he was also "concerned" with the "mysterious decline" in Kara-Murza's health, adding that he is "monitoring the situation."

John Tefft, the U.S. ambassador to Russia, said: "We are concerned about Vladimir Kara-Murza and urge that he receive the best medical care now. Our thoughts are with him and his family."

U.S. State Department spokesman Jeff Rathke told a May 28 briefing in Washington that American officials "have seen reports that Russian civil society leader Vladimir Kara-Murza is in critical condition at a hospital in Moscow."

"He’s in our thoughts, and we expect he’ll receive the best medical care possible. We’re following developments closely," Rathke said.

He declined to comment on whether U.S. officials are working to facilitate Kara-Murza's medical evacuation from Russia.

With reporting by RFE/RL's Russian Service, echo.msk.ru, and The New York Times