Hackers pose to be employees of the US Department of State in an try to get information since Wednesday.
The hackers associated with the Russian government are targeting American governments, think tanks and companies, say the internet security companies CrowdStrike and FireEye.
According to the two companies, the offence is a sign that the lee of Russian threat at the time of the US Congress elections is over.
The American intelligence community previously concluded that Russia was behind a series of hacks around the US presidential elections of 2016. Twelve Russians were indicted in July, including hacks against the Democratic Party.