Admiral Harry Harris, commander of the U.S. Pacific Command, told Congress that the THAAD anti-missile defense system would be operational “in the coming days.”

Speaking to the House Armed Services Committee on Wednesday, Admiral Harris said that North Korea remains the most “immediate threat” to the security of the U.S. and its allies in the Asia-Pacific region. The U.S. believes that North Korea is trying to develop a “preemptive nuclear strike capability” against American cities.

Admiral Harris said that the U.S. must assume North Korea’s claims are true. He added that the U.S. is prepared to fight tonight, if necessary. “That’s why the ROK-US alliance decided last July to deploy THAAD,” he said. He added that the THAAD system will be operational “in the coming days.”

China expressed its “grave concern” after parts of the THAAD system were moved to the deployment site in South Korea, which the U.S. claims is “purely defensive.” China’s Foreign Ministry said Wednesday that the deployment of THAAD breaks the strategic balance in the region and ratchets up the tension on the Korean Peninsula.

China strongly urged the U.S. and South Korea to cancel the deployment and withdraw the equipment, and sent a strong warning that China will take necessary actions “to safeguard its own interests.”

Admiral Harris said that the best way to reduce the rising tensions is to provide “credible combat power 24/7.” China is concerned that the increasing amounts of hard power and uncertainty in the region aggravate the situation and threaten China’s core strategic interests.

China is calling for efforts to resolve the explosive situation through dialogue and consultation, and has been working with the U.S. to try to reduce tension. Regarding the North Korea issues, Admiral Harris acknowledged that “China is doing things” and he is “encouraged” by China’s actions.