MOSCOW - Russian Foreign Minister Sergei Lavrov said on Monday the Litvinenko poisoning case was hurting ties with Britain, which sent detectives to Moscow as part of the investigation into the ex-KGB spy's death.

A car approaches terminal II of Moscow's Sheremetyevo airport, December 2, 2006. [Reuters]

Lavrov said insinuations in Britain of high-level Russian involvement in Alexander Litvinenko's death were "unacceptable," adding: "It is of course damaging our relations."

British police officers flew to Russia to widen their probe into the death of Litvinenko, who died in a London hospital on November 23 from a lethal dose of radioactive polonium 210.

Both Russia and Britain believe Litvinenko's death should not be politicized, Lavrov added. "If there are any questions, they should be put through law enforcement agencies," Interfax quoted him as saying.

In Brussels, British Home Secretary John Reid said Moscow has "assured us we'll get all the cooperation necessary."

Associates of Litvinenko have alleged either Kremlin involvement in his killing or that rogue elements in Russia's state security service were responsible.

Before he died, Litvinenko, a former Russian state security service agent who became one of President Vladimir Putin's sharpest critics in the London-based Russian emigre community, accused Putin of ordering his death.

The Kremlin has denied any role in the killing, and Kremlin opponents also find the theory of Putin's involvement improbable, noting such a high-profile killing on foreign soil could only damage him.

RADIATION CHECKS

British detectives are likely to try to interview Russian citizens who met Litvinenko at London's Millennium Hotel on November 1, the day he fell ill.

Andrei Lugovoy, a former KGB agent, says he and businessman Dmitry Kovtun met Litvinenko that day at the hotel. But Lugovoy, now back in Moscow, says they discussed a business opportunity and denies anything to do with an attempt on Litvinenko's life.

Alex Goldfarb, a London-based friend of Litvinenko, said the British investigators should see another ex-KGB agent, Mikhail Trepashkin, who had what he called "substantive information."

Trepashkin, serving a four-year sentence in an Urals prison for divulging state secrets, said in a letter last Friday that the FSB, the Russian state security service, had created a hit squad to kill Litvinenko and other enemies of the Kremlin.

Britain's Health Protection Agency said on Monday two more hotels in central London had been checked for radiation. Several other locations in the capital and some aircraft have also been checked amid a public health scare.

In addition, the Foreign Office said Britain's embassy in Moscow would be tested for radiation as a precautionary measure in the next day or two.

Among the other London locations caught up in the probe was the Parkes Hotel in upmarket Knightsbridge. The Sunday Times newspaper said this was where Lugovoy stayed when he visited London on his first of three trips in October.

The agency has so far tested 99 urine samples.

"The only urine sample that the agency has examined that has shown higher levels of polonium 210, relates to an adult family member (of Litvinenko)," it said.