The director of national intelligence said Russia and other countries, including China, North Korea and Iran, were using cyberspace to target US and its allies, and will do so in future.
The senate intelligence committee is holding a hearing on worldwide threats, and intelligence director Dan Coats said Russia was a threat to the US government, military, diplomatic, business and critical infrastructure.
Coats said Iran was also making use of its high-tech capabilities.
In 2013, an Iranian hacker intruded into the industrial control system of an American dam. In 2014, there was a data-deletion attack against a US-based casino.
Coats said China was also targeting the US government and American businesses. He added that such activities had diminished since US-China cyber commitments in 2015.