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The former Russian spy and his daughter poisoned by a military-grade nerve agent in Britain earlier this month have a slim chance of surviving, a relative said.

Viktoria Skripal, the niece of 66-year-old Sergei Skripal, told the BBC that the prognosis for her uncle and her cousin, Yulia, “really isn’t good” following the attack by a Soviet-developed nerve agent called novichok on March 4 in Salisbury.

“Out of 99 percent, I have maybe 1 percent hope,” she said. “Whatever [nerve agent] was used, it has given them a very small chance of survival. But they’re going to be invalids for the rest of their lives.”

The Skripals remain hospitalized and in critical condition after they were found unconscious on a park bench in Salisbury. A police officer exposed to the substance during the investigation was hospitalized and released last week.

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Countries across the world have joined the U.K. in blaming Russia for the attack. Many, including the United States, have taken diplomatic action against the Kremlin. At least 21 countries have expelled more than 135 Russian diplomats they suspect of being spies.

"Together we have sent a message that we will not tolerate Russia's continued attempts to flout international law and undermine our values," British Prime Minister Theresa May told Parliament

Russia has adamantly denied any involvement in the nerve agent attack.

"This is an attempt on the lives of Russian citizens on the territory of Great Britain," Russia's Foreign Ministry said. "It goes without saying that this unfriendly move by this group of countries will not go unnoticed."

On Monday, May said the Skripals may never recover from the attack, saying “their condition is unlikely change in the near future, and they may never recover fully.”

“This shows the utterly barbaric nature of this act, and the dangers that hundreds of innocent citizens in Salisbury could have faced,” she said. “We assess that more than 130 people in Salisbury could have been potentially exposed to this nerve agent.”

The remarks from Viktoria Skripal and May echo those made by a Russian scientist, Vil Mirzayanov, who once leaked Moscow’s secret experimentation with novichok.

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Mirzayanov, 83, said earlier this month that the nerve agent, developed in the early 90s during the end of the Cold War, is “10 times” more powerful that other nerve agents like sarin or VX.

“The people are gone – the man and his daughter. Even if they survive they will not recover,” he told AFP a week after the attack in Salisbury.

He told Reuters that the nerve agent attacks the nervous system, making it impossible for victims to breathe and causing unimaginable pain.

“It’s torture,” he said. “It’s absolutely incurable.”

The attack on the Skripal’s is reminiscent of the infamous assassination of Alexander Litvinenko, a former intelligence officer who defected to London in 2000 after publically accusing his superiors of hatching a plot against a Russian oligarch.

While living in London, Litvinenko fell ill in November 2006 and died soon after. His death was ultimately attributed to drinking tea poisoned with radionuclide polonium-210.

A judicial inquest ruled in 2016 there was a “strong probability” Litvinenko’s death was a Russian intelligence operation that was probably approved by President Vladimir Putin.

The Organization for the Prohibition of Chemical Weapons is currently conducting a probe into the nerve agent used against the Skripals. Officials said this week it could take two to three weeks to complete laboratory analysis on the samples.

The Associated Press contributed to this report.