The Pentagon is intensifying its attacks on Russia’s power grid in the latest sign of a growing cyber war between the U.S. and the Kremlin.

The U.S. has infiltrated Russia’s electric power grid among other unnamed targets, inserting American malware into the systems in response to heightened Russian cyber aggression and political meddling, including efforts to influence recent U.S. elections, according to the New York Times.

Although the Times provided few specific details on the attacks, officials said U.S. malware has the potential to cripple Russia’s electric infrastructure and is unprecedented in terms of its reach and aggressiveness.

The move is intended as a warning to Russia and would also allow the U.S. to retaliate quickly against Russian provocation.

The warning strike was authorized by U.S. Cyber Command, which was granted extended power to conduct cyber “clandestine military activity” in order to “deter, safeguard or defend against attacks or malicious cyberactivities against the United States” last year by President Trump and congress. That authorization followed concerns that the administration needed to respond more aggressively to Kremlin-ordered cyber attacks and hacking campaigns.