UK demands Russia release Navalny after 'appalling' arrest

LONDON, Jan 18 (Reuters) - Britain on Monday demanded Russia immediately release Kremlin critic Alexei Navalny and said Moscow should explain how he was attacked with a chemical weapon.

"It is appalling that Alexei Navalny, the victim of a despicable crime, has been detained by Russian authorities. He must be immediately released," Foreign Secretary Dominic Raab said.

"Rather than persecuting Mr Navalny Russia should explain how a chemical weapon came to be used on Russian soil."

Russian police detained Navalny on arrival in Moscow on Sunday after he flew home to Russia from Germany for the first time since he was poisoned last summer. (Reporting by Guy Faulconbridge; editing by Sarah Young)