Nearly two dozen European countries have expelled hundreds of Russian government personnel from embassies and consulates since Russia invaded Ukraine in late February and more recently was accused of war crimes against civilians. A significant number are probably spies posing as diplomats, according to U.S. and European officials.

Russia depends on those operatives to gather intelligence inside the countries where they serve, so the expulsions could dismantle large parts of Moscow’s spy networks and lead to a dramatic reduction in espionage and disinformation operations against the West, current and former officials said.

“The intelligence war with Russia is at full swing,” said Marc Polymeropoulos, a retired CIA officer who oversaw the agency’s clandestine operations in Europe and Russia. “This … will prove to be a significant dent in Russian intelligence operations in Europe.” Officials said it appeared to be the largest ever coordinated expulsion of diplomats from Europe.