"I cannot judge how it affects [relations] on the British side," Sergei Lavrov said, adding that attempts to make the case a political sensation are futile.
Litvinenko, 43, an outspoken critic of President Vladimir Putin's administration and a close associate of exiled oligarch Boris Berezovsky, died in a London hospital November 23. His body was found to contain a lethal dose of polonium-210, a radioactive isotope.
Traces of polonium-210 were also found at a dozen sites in London and on British Airways aircraft flying the London-Moscow route.
British police said Wednesday that they will investigate Litvinenko's case as a murder, given the preliminary results of the forensic examination.
"We have always been ready to assist the investigation," Lavrov said, adding that Russia accepted British investigators as soon as Britain forwarded a relevant request.
British investigators arrived in Moscow Monday to interview people who met with Litvinenko around the time of his reported poisoning by radiation in early November.
