Pale, gaunt and ghost-like, the former KGB agent who is fighting for his life

Gaunt and sallow, with wires snaking from his chest to banks of medical monitors, Alexander Litvinenko is in the words of his friends "a ghost".

The full effects of the toxic metal thallium on the former KGB lieutenant-colonel, who became a strident critic of Vladimir Putin's government, were made public yesterday in pictures at his bedside in a London hospital.

The 41-year-old has lost his mousey blond hair. His skin has been yellowed by kidney damage and 19 days of vomiting are evident in his drawn features and thinned lips.

Alex Goldfarb, a close friend and director of the International Foundation for Civil Liberties, said: "He is a ghost, he looks like a cancer patient. He is a man who never smoked and never drank. Now he cannot swallow, he is very weak and must be fed by tube."

Viktor Ilyukhin, deputy chairman of the Russian parliament's security committee, yesterday said he could "not exclude the possibility" that Russian authorities were behind the poisoning. "That former KGB officer had been irritating the Russian authorities for a long time and possibly knew some state secrets," he told The Sun. "So when our special services got the chance to operate not only inside but outside the country, they decided to get rid of him."

But the Kremlin yesterday dismissed claims that Russia's Federal Security Bureau (FSB, the KGB's successor) was responsible for the poisoning as " sheer nonsense".

Scotland Yard said last night that its anti-terrorist branch was in charge of the investigation into the poisoning, indicating that detectives were treating the incident as an attempted assassination.

The Russian agent fell ill on 1 November after meeting an Italian academic and KGB expert, Mario Scaramella, at a central London sushi restaurant. The Independent has learnt that Mr Scaramella met Mr Litvinenko at short notice after a threat to his own life.

Detectives were focusing on an encounter earlier that day at a London hotel between Mr Litvinenko and two unnamed Russians, one a former KGB officer.

Toxicology tests have shown that Mr Litvinenko ingested an unknown quantity of thallium, a tasteless and odourless powder which attacks the nervous system and multiple organs. A lethal dose of less than a quarter of a teaspoon can be easily administered into food or drink.

Up to five armed police officers were standing guard outside the intensive care ward at University College Hospital in central London. Mr Litvinenko, who has been given a 50-50 chance of survival, was moved to the ward after doctors warned that he could deteriorate suddenly.

Mr Litvinenko, who has allied himself with London-based Chechen leaders such as Akhmed Zakayev, has claimed he was targeted by his former employers on Moscow's orders after he began investigating the murder of the dissident journalist Anna Politkovskaya, outside her Moscow apartment last month.

Dmitry Peskov, a senior Kremlin spokesman, said: "We cannot comment on what happened to Litvinenko, and we don't consider it possible to comment on the statements accusing the Kremlin because it is nothing but sheer nonsense. "

It is understood that police are liaising with MI5 and MI6 in their investigation, which is being controlled by Deputy Assistant Commissioner Peter Clarke, head of the anti-terrorist branch. A spokesman said: "We are making a number of extensive inquiries to determine the cause of his condition, including toxicology tests, interviewing possible witnesses ... and examining CCTV footage."

It emerged yesterday that Mr Litvinenko, who fled to Britain in 2000 and sought political asylum, held at least two meetings on the day he fell ill. Hours before he met Mr Scaramella in Piccadilly, the former FSB organised crime specialist met two men for tea in a London hotel.

The former KGB officer and MI6 double agent Oleg Gordievsky, a friend of Mr Litvinenko, said that one of the men was a former KGB agent who is a member of the circle surrounding the oligarch Boris Berezovsky, who is based in Surrey. There is no suggestion that Mr Berezovsky knew of the meeting.

Mr Berezovsky has close links with Mr Litvinenko and financed a book in 2001 alleging that the FSB was responsible for blowing up apartment blocks in Moscow in attacks blamed on Chechen separatists.

Mr Gordievsky said: "There was an earlier meeting at a hotel. They took tea. The British police have been made aware of this. It is all very suspicious."

The revelation of the hotel meeting came as further details emerged of why Mr Scaramella ­ whose many areas of activity include service as an investigating magistrate near Naples ­ met Mr Litvinenko at short notice on 1 November.

The Independent has been told that two days earlier Mr Scaramella received two e-mails threatening his life and that of Senator Paolo Guzzanti, the politician who appointed Mr Scaramella to the Mitrokhin commission investigating KGB activities during the Cold War.

The e-mails accused both men of falsifying the activities of the KGB and warned of the "necessity to use force" against them. The messages ­ seen by The Independent ­ name a Russian agent who is said to be planning to attack Mr Scaramella and say the same man was "presumably involved" in Ms Politkovskaya's murder. It has been presumed that Mr Litvinenko met his Italian contact to discuss this link with the Politkovskaya case.

But it is thought the meeting was held so Mr Scaramella could ask the opinion of the former FSB officer about the credibility of the threat.

A source in Italy said that Mr Scaramella was adamant he had nothing to do with the poisoning.

Who's linked to the Russian poisoning case

BORIS BEREZOVKSY

The former mathematician and scientist benefited from perestroika in the early 1990s by selling cars. He was the first billionaire of the post-Communist era, with interests from oil to aviation. He backed Vladimir Putin to become President in 2000, but fell out with him and fled into exile in Surrey. He is wanted in Russia for corruption, which he denies.

VLADIMIR PUTIN

The Russian President since 2000, Putin was a member of the KGB for 15 years until 1990, spending much of that time based in East Germany. It was while he was head of its successor, the FSB, that Litvinenko claimed he was ordered to murder Berezovsky. Putin has been criticised for an increasingly authoritarian stance.

MARIO SCARAMELLA

A self-styled environmental consultant, Scaramella is an expert on the KGB who is said to have links to the Italian intelligence service. He was part of a government commission into the Cold War activities of the KGB in Italy. Scaramella claims he was meeting Litvinenko in London to seek his advice on an apparent death threat.

AKHMED ZAKAYEV

The former actor was minister of culture in Chechnya and a field commander in the first war with Russia. He was granted asylum in Britain in 2003 after being wounded, and fought off an extradition request from Russia. A court ruled that the request was politically motivated. He is foreign minister for Chechnya's government-in-exile.

OLEG GORDIEVSKY

One of MI6's most successful double agents, Gordievsky was the KGB's second-in-command in London. He was smuggled out of the Soviet Union in 1985 after being recalled by the KGB and became one of the most high-ranking defectors of the Cold War. He is a friend of Litvinenko and an authority on the tactics of Russian security.