Several foreign governments have hacked into U.S. energy, water and fuel distribution systems and might damage essential services, the top national security official said.

Those intrusions have left the U.S. vulnerable to a cyber attack that will cause significant loss of life or physical damage one day, National Security Agency Director Admiral Michael Rogers told the House intelligence committee at a hearing in Washington on Wednesday. Rogers said such an attack will occur during his tenure.

“This is not theoretical,” Rogers said. Hacking attacks on U.S. networks are “literally costing us hundreds of billions of dollars” and will have “truly significant, almost catastrophic, failures if we don’t take action.”

Rogers is one of the highest-ranking U.S. officials to warn about looming cyber attacks. The warning is significant because it demonstrates that hacking attacks against U.S. companies and agencies are escalating in seriousness despite awareness about them and efforts to combat foreign intruders.

Lawmakers are aware of the seriousness, despite the inability of Congress to pass cybersecurity legislation that companies and government officials have said is essential to warding off attacks.

‘Under Attack’

A Chinese military officer indicted by the U.S. in May allegedly gained access to a utility’s computers while on a scouting mission for information that China could use to wage war. The breach was followed by a Homeland Security Department warning to utilities in October to be on the lookout for malicious software that cybersecurity companies have connected to Russia.

“I fully expect that during my time as the commander we are going to be tasked to help defend critical infrastructure within the United States because it is under attack by some foreign nation or some individual or group,” Rogers said.

“This will be truly destructive if someone decides this is what they want to do.”

The NSA director didn’t identify any countries but didn’t dispute that China, Russia and Iran have infiltrated U.S. critical infrastructure to carry out destructive attacks. Rogers said he also sees a “troubling” trend in which foreign governments hire criminals to carry out hacking attacks on U.S. networks in order to obscure their involvement.