The embassy said that for U.K. authorities it was purely a criminal matter, and that the case had provoked health concerns for hundreds of Londoners.
Russian Foreign Minister Sergei Lavrov said earlier: "We see attempts by the British side to use the criminal case and the necessity of professional investigation to fan a political campaign: we are against this. The relevant authorities should deal with it."
The U.K. has officially demanded that Moscow extradite a Russian national, Andrei Lugovoi, who they accuse of murdering ex-FSB officer Alexander Litvinenko last November. Litvinenko received British citizenship shortly before his fatal poisoning.
A British Embassy spokesman said "We have repeatedly said that Litvinenko's death is a criminal case of key importance. We now expect an official and constructive response to our request on the extradition of Mr Lugovoi, so that the case can be transferred to the appropriate authority, an independent British court."
The U.K. Foreign Office issued a statement saying Britain has "no desire to aggravate diplomatic relations" with Russia over the case. "We have consistently said the murder of Mr Litvinenko is a very serious criminal matter," the statement said.
