LONDON — A top British intelligence official said on Wednesday that European countries have this year expelled hundreds of Russian officials who are believed to be spies.

"This year, a concerted campaign has seen a massive number of Russian officials expelled from countries around the world, including more than 600 from Europe - over 400 of whom we judge are spies," Ken McCallum said in a speech at MI5’s headquarters.

McCallum said that this is "the most significant strategic blow" against the Russian intelligence services in recent European history in addition to coordinated waves of sanctions.

"We've continued to work intensively to make the UK the hardest possible operating environment for Russian covert action," he stated.

McCallum also underlined that Britain also refused 100 diplomatic visa applications on national security grounds.

"The UK must be ready for Russian aggression for years to come," he added. — Agencies