China and other foreign entities have the capacity to shut down computer systems that control key U.S. infrastructure, including power and water systems, the NSA chief said Thursday.

Adm. Michael Rogers made the comments while testifying before a congressional panel. Rogers said the U.S. had detected malware from China and “probably one or two” other countries on systems that have critical importance to the U.S.' ability to provide key services.

“It enables you to shut down very segmented, very tailored parts of our infrastructure that forestall the ability to provide that service to us as citizens,” Rogers said, according to a report from CNN

Rogers also told the committee that U.S. adversaries were performing “reconnaissance” on American systems regularly, and that it is only a matter of when, not if, we are going to see something dramatic,” according to the Associated Press.

Rogers' testimony is the first time that the nation's top cyber-security official has confirmed the possibility of such serious attacks taking place.

While Rogers did not name any other countries besides China in his testimony, he did not dispute that Russia and Iran had also infiltrated U.S. critical infrastructure to carry out attacks, according to Bloomberg

Experts cited by Fox News said the U.S. is similarly capable of disrupting the systems of foreign countries, and claimed this amounted to a mutual deterrent.

China has been implicated in a large number of hacking attacks against U.S government departments and private companies. Earlier this month, a hacking attack on the U.S. National Oceanic and Atmospheric Administration was attributed to China by some lawmakers.

Likewise, a major cyber-security breach earlier this month at the U.S. Postal Service was also suspected to be the work of Chinese hackers. 

In May of this year, the U.S. filed criminal charges against five members of China's People's Liberation Army for alleged hacking offenses.

In October, the FBI warned that hackers backed by China's government were launching cyberattacks against U.S. businesses. China branded the allegations as “unfounded.”

Rogers' testimony comes just days after the USA Freedom Act -- a bill that would have limited the agency's surveillance powers -- was voted down in the U.S. Senate. While the bill would have limited the NSA's surveillance abilities, it also included an extension of the controversial Patriot Act, according to Zdnet