LONDON — A British Cabinet minister accused President Putin of Russia of “attacks on individual liberty and on democracy” and acknowledged yesterday that relations with Moscow were strained after a former KGB agent was poisoned to death in London.

The government’s Northern Ireland Secretary, Peter Hain, said Mr. Putin’s tenure had been clouded by incidents “including an extremely murky murder of the senior Russian journalist” Anna Politkovskaya.

They were the strongest comments leveled at Moscow since former KGB agent and Kremlin critic Alexander Litvinenko died Thursday from poisoning by the radioactive element polonium-210. In a dramatic statement dictated from his hospital bed and read outside the hospital after his death, Litvinenko accused the “barbaric and ruthless”Mr. Putin of ordering his poisoning.

“His success in binding what is a disintegrating nation together with an economy that was collapsing into Mafioso style chaos, his success in that must be balanced against the fact there have been huge attacks on individual liberty and on democracy,”Mr. Hain said of Mr. Putin. “And it’s important that he retakes the democratic road in my view,” he told British Broadcasting Corp. He agreed when asked if relations with Moscow were at a “tricky stage.”

British officials have so far avoided blaming Moscow for Litvinenko’s death, and Mr. Hain did not comment directly on the case.

But opposition leaders demanded yesterday that the government explain what it knows about the poisoning and, in particular, how the deadly nuclear material used to poison the 43-year-old Litvinenko found its way into Britain.

Litvinenko told police that he believed he was poisoned November 1 while investigating the October slaying of Politkovskaya, another critic of Mr. 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 a “suspicious death,” rather than a murder. They have not ruled out the possibility that Litvinenko may have poisoned himself.

Litvinenko’s friends and allies in London’s Russian immigrant community blamed Mr. Putin, who has denied any involvement and called the death a tragedy. Russian officials could not be reached for comment yesterday on Mr. Hain’s remarks.

Home Secretary John Reid 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 today 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 into 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,” the Conservative law-and-order spokesman, David Davis, said.

The ex-spy’s death sparked a huge public-health alert, with authorities preparing to test scores of people who may have come into contact with Litvinenko for traces of radiation.

Radiation was found at Litvinenko’s London house, a sushi bar where he met a contact November 1, and a hotel that he visited earlier that day, police said.