(CNN) — Russian-speaking hackers are behind cyberattacks on government agencies, a senior U.S. official told reporters Thursday.

Earlier Thursday, the US administration moved to contain the fallout from the attack, which has affected systems around the world.

The US official, citing expert estimates, pointed out that several hundreds of companies and institutions in the US and government agencies could be affected by the cyber attack, and that the hackers did not demand ransom from official institutions.

Last week, a Russian-speaking hacking group called CLOP claimed responsibility for attacks on the BBC, British Airways, oil company Shell, and the states of Minnesota and Illinois. .

Meanwhile, a Department of Energy spokesperson told CNN that his department was among government agencies hacked Thursday, and it was unclear what other agencies were affected by the attack.

A US Cybersecurity and Infrastructure Security Agency (CISA) official declined to say what or how many agencies were affected.
Eric Goldstein, assistant administrator for the Cybersecurity Agency, said in a statement to CNN that the agency “provides support to multiple agencies that have been compromised.”

The breach is in addition to a string of cyber attacks targeting major universities and US government officials that began two weeks ago.

The hacking piles pressure on U.S. officials who have vowed to crack down on attacks that have disrupted schools and hospitals across the country.