The United States faces "serious and significant" threats within cyberspace, the White House's top counter-terrorism advisor said Sunday, adding it was an issue of national security.

"The threats and the vulnerabilities within the cyber domain are serious and significant," John Brennan told NBC, adding a cybersecurity board had been set up at the White House.

"It's a very complex and complicated challenge, but we are working very closely with the private sector."

Last month a row over Internet freedom erupted between China and the United States as Beijing denied any state involvement in cyberattacks on Internet search engine Google.

President Barack Obama said he was "troubled" by Google's statements it had been attacked by China-based hackers, and demanded official answers.

"We're looking at these issues from the standpoint of espionage, from governments, from different individuals, whether they be hackers or terrorist organizations," Brennan said.

"National security is something that is at risk. That's why what we're trying to do is to ensure that our networks, our government networks, our private sector networks have the ability to withstand these attempts to hack in."

The US House of Representatives last week overwhelmingly approved a bill aimed at protecting the Internet and vulnerable computer networks by funding cybersecurity research and training.