LONDON – A former Russian spy poisoned in Britain and now hospitalized under guard may have been targeted because of his criticism of former colleagues and his investigation into the killing of a prominent anti-Kremlin journalist, friends and fellow dissidents said Sunday.

Col. Alexander Litvinenko, a former KGB agent, said earlier this week that he fell ill on Nov. 1 after a meal with a contact who claimed to have details about the slaying of Anna Politkovskaya, the Russian journalist gunned down last month in Moscow.

A doctor treating Litvinenko told the British Broadcasting Corp. that tests showed he was the victim of poisoning by thallium – a toxic metal found in rat poison. He is under armed guard at University College Hospital in London.

“He’s got a prospect of recovering, he has a prospect of dying,” said Dr. John Henry, a clinical toxicologist who treated Ukrainian President Viktor Yushchenko in 2004 after he was poisoned during his presidential election campaign. Henry said thallium can cause organ failure and damage to the nervous system, and that just one gram can be lethal.

In an interview with the Sunday Times before his condition worsened, Litvinenko described how he had lunch with an Italian contact who claimed to have information on Politkovskaya’s killing, which has not been solved. British news outlets identified the contact as Mario Scaramella, an Italian academic who helped investigate KGB activity in Italy during the Cold War.

“They probably thought I would be dead from heart failure by the third day,” Litvinenko is quoted as saying in the Sunday Times. “I do feel very bad. I’ve never felt like this before – like my life is hanging on the ropes.”

Police have opened an investigation into the poisoning, a spokesman said.

Litvinenko left Russia for Britain six years ago and has become an outspoken critic of the Kremlin. In a 2003 book, “The FSB Blows Up Russia,” he accused his country’s secret service agency of staging apartment-house bombings in 1999 that killed more than 300 people in Russia and sparked the second war in Chechnya.

Boris Berezovsky, a Russian dissident and tycoon who was at Litvinenko’s bedside on Friday, said he suspects Russia’s intelligence services of the poisoning.

“It’s not complicated to say who fights against him,” Berezovsky said in a telephone interview. “He’s (Russian President Vladimir) Putin’s enemy; he started to criticize him and had lots of fears.”

Another friend, Alexander Goldfarb, who organized Litvinenko’s immigration to Britain, said FSB agents had threatened him in the past.

“He looks like a ghost,” Goldfarb said. “He’s a very fit man, he never smoked, he never drank, he would run five miles a day – but now he has lost all his hair, he has inflammation in the throat, so he cannot swallow.”

Russian authorities did not immediately comment on the allegations.

Kremlin critics claim poisoning – which is extremely hard to prove – is a common Soviet-era practice that seems to have reappeared since Putin, an ex-KGB officer, became president.