China said it was opposed to any deployment of nuclear weapons by Japan and South Korea in response to North Korea's repeated missile tests and its quest for a military "equilibrium" with the US.
China's ambassador to the US, Cui Tiankai, said the potential spread of nuclear weapons would not bring security to the highly-tensed region.
"It could only make things much worse. We are certainly opposed to the existence of nuclear weapons anywhere on the Korean peninsula or anywhere," the Hong Kong-based South China Morning Post quoted Cui as having told reporters in Washington on Friday.
The comments came on a day North Korea launched its second intermediate-range missile over the Japanese territory in less than a month. The missile test was the first after Pyongyang tested its sixth and largest nuclear device on September 3.
Experts assessing the data now increasingly believe the latest nuclear test by North Korea to be a hydrogen bomb.
The North Korean state media said the reclusive nation's aim was to seek an "equilibrium" of military force with the US after an emergency meeting of the UN Security Council again condemned the Pyongyang's nuclear and missile tests.
The tests have resulted in calls for deployment of US nuclear weapons by American allies South Korea and Japan.
Ambassador Cui said China understood South Korea's fears.
"We are willing to help them to solve these concerns on the condition of not risking China's security interests," he said, apparently referring to US deployment of the Terminal High Altitude Area Defence (THAAD) weapons in South Korea.
Beijing firmly opposes THAAD deployment because its powerful radars could monitor China's movement of missiles and their deployment.
The deployment of nuclear weapons in South Korea and Japan will bring them to the doorstep of China.