BRUSSELS—European relations with Moscow, which went into a tailspin over Ukraine in 2014, are deteriorating anew as Russian bombing of the Syrian city of Aleppo sweeps aside moves to ease tensions.

As European Union governments prepared to discuss next week how to step up their response to the Syrian bloodshed, Russian President Wednesday, accusing the U.S. and Europe of unfairly blaming Moscow for the breakdown of a Syrian cease-fire.

He...