The FBI announced Tuesday that it has disrupted a network of hacked computers that Russian spies have used for years to steal sensitive information from at least 50 countries, including NATO governments.

The action appears to be a major blow to Russia's domestic intelligence service, the FSB, which has allegedly used the sophisticated hacking tool to infiltrate US and Western diplomatic and military agencies for nearly two decades. It's the latest move by the Justice Department to more aggressively target foreign spying and criminal rings using custom-built FBI tools.

The FBI used a court order on Monday to cut off the Russians access to the network of computers in the US that the hackers were using to spirit the stolen information around the world and back to Russia, US officials said. The FBI operation and US public advisories on the hacking tool would make it "difficult or and untenable" for the FSB to effectively use it again, a senior FBI official said in a call with reporters Tuesday.

The Russian Embassy in Washington did not immediately respond to a request for comment.

The Russian hacking group that the FBI targeted, known as Turla, is widely believed by experts to be one of the most elite cyber-espionage units in the Russian intelligence services. Turla's tools are associated with a big breach of US military networks in the mid-to-late 1990s and a hack of US Central Command in 2008.

In recent years, the hackers have been observed burrowing into the networks of foreign ministries and parliaments in Eastern Europe to collect intelligence on Russian adversaries.

This story is breaking and will be updated.