MOSCOW (AP) — British Prime Minister David Cameron insisted Monday that Russia and Britain can overcome the sharp differences in their relations — even the 2006 poisoning death of a Kremlin critic in London — to seal new trading ties and help promote world stability in the wake of the Arab uprisings.

Cameron was in Moscow for the first visit to Russia’s capital by a British leader in six years, meeting with President Dmitry Medvedev, and holding the first talks by any British official with Prime Minister Vladimir Putin in more than four years.

Ties between Britain and Russia soured over the 2006 poisoning death of dissident ex-Russian security agent Alexander Litvinenko in London. Litvinenko made a deathbed statement accusing Putin of authorizing his killing.

Russia has refused British requests for the extradition of the chief suspect in the case, ex-KGB agent Andrei Lugovoi, who denies involvement.

Following talks at the Kremlin, Medvedev told Cameron there was no prospect of Lugovoi facing a British court because the Russian constitution prohibits the extradition of a Russian citizen.

“This will never happen, no matter what the circumstances,” Medvedev said during a news conference with Cameron. “We all have to learn to respect our legal frameworks.”