General John Hyten, who leads US Strategic Command (STRATCOM), told lawmakers the US has "not gone nearly far enough" in the cyber domain, also noting that the military still lacks clear rules of cyber engagement.

"We have to go much further in treating cyberspace as an operational domain," Hyten told the Senate Armed Services Committee.

"Cyberspace needs to be looked at as a warfighting domain, and if somebody threatens us in cyberspace we need to have the authorities to respond."

Hyten noted, however, that the US had made some progress in conducting cyber attacks on enemies in the Middle East, such as the Islamic State group.

His testimony comes weeks after General Curtis Scaparrotti, commander of NATO forces in Europe, warned that US government agencies are not coordinating efforts to counter the cyber threat from Russia, even as Moscow conducts a "campaign of destabilization."

And last month, Admiral Michael Rogers, who heads both the NSA -- the leading US electronic eavesdropping agency -- and the new US Cyber Command, said President Donald Trump had not yet ordered his spy chiefs to retaliate against Russian interference in US elections.

The US has accused Russia of actively interfering in the 2016 presidential election, stealing Democratic party communications and pushing out disinformation through social media.

It also accuses Moscow of stealing hacking secrets of the US intelligence community -- while US cyber security investigators have accused the Russian government of a sustained effort to take control of critical US infrastructure systems including the energy grid.

Hyten added the military needs clear authorities and rules of engagement so operators know when and how to respond to attacks.

"We need to have specific rules of engagement in cyber that match the other domains that we operate in," Hyten said.

"We need to delegate that authority all the way down so we can deal with threats that exist that challenge the United States."