President Barack Obama entered the fray Wednesday on cyber attacks from China, saying some intrusions affecting US firms and infrastructure were "state sponsored."

The comments appeared to step up the rhetoric against China following similar remarks from other members of the US administration.

"What is absolutely true is that we have seen a steady ramping up of cyber security threats. Some are state sponsored. Some are just sponsored by criminals," Obama said in an interview with ABC News aired Wednesday.

"We've made it very clear to China and some other state actors that, you know, we expect them to follow international norms and abide by international rules.

"And we'll have some pretty tough talk with them. We already have," Obama said, complaining that billions of dollars and industrial secrets were lost due to hacking.

The comments by the president came after a series of warnings from top US security officials that Washington would not stand idly by in the face of these threats.

General Keith Alexander, who heads the US National Security Agency and Cyber Command, told lawmakers Tuesday that the military is creating units that would have offensive capabilities in cyberspace as part of efforts to protect US infrastructure.

"This is an offensive team that the Defense Department would use to defend the nation if it were attacked in cyberspace," Alexander told a Senate panel.

"Thirteen of the teams that we're creating are for that mission set alone."

James Lewis, a cybersecurity specialist at the Center for Strategic and International Studies, said the heightened rhetoric suggests Washington's patience has worn thin with China and some other governments after numerous diplomatic initiatives.

"There is some intelligence which hasn't been made public that points toward China as the major actor in economic espionage," Lewis told AFP.

"Embarrassing the Chinese doesn't work, and this raises the ante."

Lewis said the new comments suggest the US military could disrupt hackers from China or elsewhere if they are involved in "attacks that could cost American lives or could do significant damage to the economy."

"The military has a new role and it strikes me as legitimate," Lewis said.

Obama and national security officials met earlier in the Situation Room to discuss cybersecurity with chief executives from major companies in sectors including energy, telecom, finance and defense.

"The president and the CEOs discussed the increasing cyber threats to our critical infrastructure and our economy," according to a White House official.

They spoke about the need for cybersecurity legislation and ways for the private and public sectors to collaborate on defenses.

The president also discussed a recent executive order on cybersecurity.

China said it was willing to cooperate with the United States and others to combat hacking and also noted that it was a victim of such attacks.

"What is necessary in cyberspace is not war, but rather regulation and cooperation," foreign ministry spokeswoman Hua Chunying said.

Last month, a report from US security firm Mandiant said a unit of China's People's Liberation Army had stolen hundreds of terabytes of data from at least 141 organizations, mostly based in the United States.

CIA Director John Brennan told a panel on Tuesday that "the seriousness and the diversity of the threats that this country faces in the cyber domain are increasing on a daily basis."

US national intelligence chief James Clapper said that there was "a remote chance of a major cyber attack against US critical infrastructure systems during the next two years that would result in long-term, wide-scale disruption of services, such as a regional power outage."

But he noted that "isolated state or non-state actors might deploy less sophisticated cyber attacks," which could affect "some poorly protected US networks that control core functions, such as power generation."

National Security Adviser Tom Donilon warned China on Monday against cyber threats.

Donilon said that US businesses are growing more concerned "about sophisticated, targeted theft of confidential business information through cyber-intrusions emanating from China at a very large scale."

"Beijing should take serious steps to investigate and put a stop to these activities," he said.