British Prime Minister David Cameron is in Moscow on the first visit by a British leader to Russia in six years.

Mr. Cameron is expected to encourage closer trade ties with Russia. Relations between the two countries soured in 2006 after a Russian ex-security agent, Alexander Litvinenko, died of poisoning in London.

So far, Russia has refused British requests to extradite Andrei Lugovoy, a Russian suspected of being responsible for Litvinenko's death.

Mr. Cameron is to meet Monday with Russian President Dmitry Medvedev, and is expected to raise the case during their talks. Mr. Cameron is also scheduled to meet with Russian Prime Minister Vladimir Putin. The meeting with Mr. Putin will be the first by a British official since 2007.

Trade appears to be at the top of Mr. Cameron's agenda. Traveling with the British prime minister is a group of more than 20 business leaders including BP senior executive Robert Dudley.

Speaking to students at Moscow University Monday, Mr. Cameron stressed being candid about the differences that still separate the two nations.