Russia to expel Ukrainian diplomat, prompting vow of retaliation from Kyiv

Disagreement over Alexander Sosonyuk, who was allegedly caught trying to obtain sensitive information, escalates tensions after troop buildup

Russia on Saturday said it would expel a Ukrainian diplomat, prompting an immediate pledge of retaliation from Kyiv, further escalating tensions after Moscow's troop buildup on Ukraine's eastern flank.

The detention of a Ukrainian consul in the second city, St Petersburg, comes at a time of global concern over a possible repeat of Moscow's 2014 aggression, when Russia annexed the peninsula of Crimea and backed separatists in Ukraine's east. Moscow claimed that the diplomat had been caught red-handed" trying to obtain sensitive information.