Russian President Vladimir Putin in an interview with journalists from Group of Eight countries said London's call for the extradition of the key suspect in the murder of former Russian spy Alexander Litvinenko was "stupidity."

British prosecutors last month said they had enough evidence to charge Andrei Lugovoy, a former KGB spy, with the poisoning of Litvinenko, calling on Russia to extradite the man so he can be brought before a British court. However, the Russian constitution forbids extraditing Russian citizens.

"If they didn't know (about the constitutional prohibition) it's a low level of competence and thus we have doubts about what they're doing there. And if they knew and did this, it's simply politics," Putin said.

"This is bad and that is bad -- from all sides it's the same stupidity," Putin said.

Lugovoy, the main suspect, last month accused the British MI6 intelligence agency of having a hand in the killing.

Anglo-Russian relations have taken a beating over the spy murder; the case is expected to be tackled on the sidelines of the Group of Eight summit, which kicks off Wednesday in the German Baltic Sea resort of Heiligendamm.