A senior British government minister on Sunday accused Russian President Vladimir Putin of presiding over attacks on liberty and democracy as anti-terrorist police investigated the radiation poisoning that killed a former Soviet spy. British officials have avoided blaming Moscow for the death of Kremlin critic Alexander Litvinenko, killed by radioactive polonium-210, but opposition leaders called for a public explanation from the government of how the deadly nuclear material came to be in Britain. In the strongest comments leveled at Moscow since the ex-spy's death, Cabinet minister Peter Hain accused Putin of presiding over "huge attacks on individual liberty and on democracy" and acknowledged that relations between London and Moscow were at a difficult stage. Hain, the government's Northern Ireland secretary, said Putin's tenure had been "clouded" by incidents "including an extremely murky murder of the senior Russian journalist" Anna Politkovskaya. Hain did not comment directly on the Litvinenko case. But he told British Broadcasting Corp. television that Putin's economic achievements "must be balanced against the fact there have been huge attacks on individual liberty and on democracy and it's important he retakes the democratic road, in my view." Litvinenko, 43, a former KGB agent who was a fierce critic of Putin, died Thursday of heart failure after falling gravely ill from what doctors said was poisoning by the radioactive element polonium-210. He told police he believed he was poisoned Nov. 1 while investigating the October slaying of Politkovskaya, another critic of Putin's government. The ex-spy was moved to intensive care last week after his hair fell out, his throat became swollen and his immune and nervous systems suffered severe damage. London's Metropolitan Police said they were investigating it as a "suspicious death" rather than murder. They have not ruled out the possibility that Litvinenko may have poisoned himself. Litvinenko's friends and allies in London's Russian emigre community pointed the finger squarely at Putin. In a dramatic statement dictated from his hospital bed and read after his death, Litvinenko accused Putin - calling him "barbaric and ruthless" - of ordering his poisoning. Putin called the death a tragedy and denied involvement. Home Secretary John Reid, Britain's top law-and-order official, refused to speculate about who might have killed Litvinenko. "I don't think it's for me as a politician to be making judgments that a policeman should make," he told Scotland's Radio Clyde. The main opposition Conservative Party demanded the government make a statement in the House of Commons outlining what it knew about the case and how polonium-210 - a rare radioactive element usually produced in a nuclear reactor or particle accelerator - got to Britain. "It is essential that other dissidents living in Britain are reassured about their safety and there are also questions about how polonium-210 came to be used in Britain," said David Davis, the Conservative law-and-order spokesman. Relations between Russia and Britain have remained cool since the end of the Cold War. London has infuriated Moscow by offering refuge to self-exiled tycoon Boris Berezovsky, a Kremlin critic wanted in Russia on money-laundering charges, and Akhmed Zakayev, a representative of late Chechen rebel chief Aslan Maskhadov. In January, Russia's Federal Security Service, the FSB, accused four British diplomats of spying, showing on state-run television sophisticated communications equipment concealed in a fake rock, which it said the Britons hid in a Moscow park to use to contact Russian agents. Litvinenko's death sparked a public health alert, with authorities preparing to test hundreds of people who may have come into contact with Litvinenko for traces of radiation. Radiation was found at Litvinenko's north London house, a sushi bar where he met a contact Nov. 1 and a hotel he visited earlier that day, police said. The Health Protection Agency said 300 people have contacted officials. They will be screened and some will have their urine tested for radiation, the agency said. But officials said the risk to others was low because polonium-210 can only contaminate if it is ingested, inhaled or taken in through a wound. It could take up to a week to process the samples, the agency said in a statement. Detectives have finished their search of the sushi bar where Litvinenko met an Italian contact, Mario Scaramella. The building was being decontaminated, police said. Litvinenko's contaminated body was released to a coroner late Saturday, and government pathologists were awaiting advice on whether it was safe to perform an autopsy. On Sunday, Alexander Lebedev, a former KGB spy who is a member of the Russian parliament, said Putin's government played no part in the death. "I completely rule out the possibility of that being done on official orders from anyone in the authorities," Lebedev told Sky News. The Sunday Times newspaper reported that as he lay dying, Litvinenko named an alleged Russian agent he feared had been sent to hunt him down, and said he previously complained to police that the man had harassed him at home. Litvinenko claimed the Russian agent was not directly involved in his poisoning but had been sent to monitor his activities, the newspaper said. Police said they could not immediately confirm whether officers would seek to interview the alleged Russian agent. The Foreign Office said it has asked Moscow for help with the investigation. Litvinenko worked for the KGB and its successor, the FSB. In 1998, he publicly accused his superiors of ordering him to kill Berezovsky and spent nine months in jail from 1999 on charges of abuse of office. He was later acquitted and in 2000 sought asylum in Britain.