In case you've been living in a cave with your eyes shut and your fingers in your ears...

Diplomatic relations between Russia and Britain have officially collapsed.

Washington Post: Russia expelled 4 British diplomats on Thursday, retaliating in-kind just days after officials in London kicked 4 Russians out of the country in protest over the progress of a murder investigation.

The tit-for-tat expulsions stem from Moscow's refusal to extradite the Russian man accused of poisoning Alexander Litvinenko, a former Russian domestic intelligence officer, in London last November. The incident unnerved Londoners because it involved the use of a radioactive element later found in other parts of the city, and now has become a full-fledged diplomatic row.

U.S. Secretary of State Condoleezza Rice said Thursday that Russia should extradite Andrei Lugovoy, the man accused by Britain of murdering Litvinenko. The EU has expressed its "disappointment" at Russia's lack of cooperation.

Lugovoy is accused of using polonium-210 to kill Litvinenko, a fierce critic of Putin. Litvinenko, a former officer in the FSB, a KGB successor agency, fled to Britain in 2000, where he became a citizen. The case is particularly charged because Litvinenko suffered a slow and gruesome death. In addition, 100s of Londoners feared they were exposed to the radioactive substance and underwent tests amid panic in the city last November.