MOSCOW: Russia on Thursday officially refused a request from Britain to extradite the chief suspect in the murder last year of a former Russian agent in London, the Russian prosecutor general's office said.

Russia's constitution prevents the extradition of Russian citizens, the prosecutor's office said in a statement.

“It is therefore not possible to satisfy the request from the British side for the extradition of Andrei Lugovoi,” the statement added.

British prosecutors say Lugovoi used a rare radioactive isotope to poison Alexander Litvinenko, a former Russian intelligence agent turned Kremlin critic, during a meeting in London in November.

Lugovoi has repeatedly denied any involvement in Litvinenko's murder. The statement said Russian prosecutors could investigate Lugovoi “if the British side makes the corresponding inquiry and offers the necessary material for a criminal case.” The prosecutor general's office “underlined its readiness to offer assistance in criminal inquiries to the relevant authorities in Britain under international agreements,” the statement said.

The murder case has severely strained relations between the two countries. Litvinenko had received political asylum and then citizenship in Britain. British authorities sent their extradition request to Russia five weeks ago.—AFP