FACTBOX: Key facts about suspect Andrei Lugovoy

(Reuters) - Britain said on Monday it was expelling four Russian diplomats over Moscow's refusal to extradite the main suspect in the murder of Alexander Litvinenko.

Following are some key details on the suspect, former state security agent Andrei Lugovoy:

* Lugovoy was a KGB officer from the late 1980s when he worked in the department that protected senior Soviet officials. He left the FSB, the KGB's successor, at the end of 1996 and later worked as head of security for tycoon Boris Berezovsky.

* Lugovoy met Litvinenko at the Millennium Hotel in Grosvenor Square on November 1 along with another Russian, Dmitry Kovtun. Later that day, Litvinenko complained of feeling ill and was admitted to hospital shortly afterwards. He died three weeks later, on November 23, from polonium 210 poisoning.

* Lugovoy was treated last year in an isolated unit at a Moscow hospital that treated the victims of the 1986 Chernobyl nuclear disaster. He refused to say what he was being treated for but some media reported he had radiation poisoning.

* Lugovoy has denied any involvement in Litvinenko's death and lashed out at the British media for making him out to be "a monster". Russia has refused to extradite Lugovoy to face charges of killing Litvinenko.

* Lugovoy says he had known Litvinenko casually for about 10 years and that in 2005 Litvinenko called him offering contacts. He said Litvinenko was helping him in talks with British businesses.