MOSCOW, July 19 (RIA Novosti) - British Ambassador to Russia Anthony Brenton has arrived at the Foreign Ministry to discuss an ongoing extradition row that escalated earlier in the week with the U.K.'s expulsions of four Russian diplomats.

The U.K. decided to expel diplomats and suspend visa facilitation talks with Moscow after Russia refused to extradite Andrei Lugovoi, the U.K.'s key suspect in the Alexander Litvinenko murder case.

Last week, British prosecutors said they had received Russia's official refusal to extradite Lugovoi, which cited the Russian Constitution as saying Russian citizens could not be handed over to other countries, and proposed trying Lugovoi in Russia if Britain provides sufficient evidence.