Russian President Dmitry Medvedev has flatly refused to extradite a Russian suspect wanted by Britain in the polonium poisoning in London of a former Moscow agent, tarnishing British Prime Minister David Cameron's first visit to Moscow.

Mr. Cameron's trip is the first visit by a British leader to Russia in six years, and was expected to focus mainly on business ties. Relations between the two countries soured in 2006 after the former Russian security agent, Alexander Litvinenko, died in London.

Mr. Medvedev said Monday the extradition “would never happen.” His statement echoed previous refusals by Moscow to extradite Andrei Lugovoy, who London believes is responsible for Litvinenko's death.

The British prime minister said differences between the two countries should not “freeze” their relationship.

The two leaders joined to sign business deals worth about $340 million. Traveling with Mr. Cameron is a large business delegation, including top executives from BP, Royal Dutch Shell and Rolls Royce.

Mr. Cameron is to meet later Monday with Russian Prime Minister Vladimir Putin.

Speaking to students at Moscow University Monday, Mr. Cameron stressed being candid about the divisions that still separate the two nations, including disagreement on how to handle Syria.