(Recasts with U.S. statement)

By David Brunnstrom

WASHINGTON, Oct 3 (Reuters) - The United States condemned North Korea's firing of a ballistic missile over Japan as "dangerous and reckless" and pledged to defend South Korea and Japan with all America's power, but said it remained open to dialogue with Pyongyang.

"This action is destabilizing and shows the DPRK’s blatant disregard for United Nations Security Council resolutions and international safety norms," White House National Security Council spokeswoman Adrienne Watson said in statement, referring to North Korea by the initials of its official name.

She said U.S. National Security Advisor Jake Sullivan spoke with his Japanese and South Korean counterparts to discuss "appropriate and robust joint and international responses."

Sullivan reinforced the "ironclad" U.S. commitments to the defense of Japan and South Korea and said Washington would continue efforts to limit North Korea's ability to advance its prohibited weapons programs.

The missile fired on Thursday was the first to fly over Japan in five years, prompting a warning for residents to take cover and a temporary suspension of train operations in northern areas of the country.

Daniel Kritenbrink, the State Department's assistant secretary for East Asian and Pacific affairs, said China needed to do more to fight sanctions evasion by North Korea in its coastal waters. He added that Beijing and Russia should work to shut down Pyongyang's procurement networks.

"The failure of the PRC and Russia to fully and completely fulfill their obligations ... has only, we fear, emboldened the DPRK in undermining the U.N. Security Council, the international rules-based order and global non-proliferation regime," he said.

Kritenbrink said that persuading North Korea to denuclearize ought to be an area of cooperation with China, but that there were some in Beijing who want to use the issue as leverage in the broader strategic rivalry with Washington.

He reiterated that Washington remained open to dialogue with North Korea without preconditions and called Pyongyang to "commit to serious and sustained diplomacy, and refrain from further destabilizing activities."

"Unfortunately... the only response we have seen thus far is an increase in the number of ballistic missile launches and other provocative actions," he said. "This is not a productive path forward, neither for North Korea or for any of us."

Kritenbrink reiterated a U.S. assessment that a resumption of nuclear testing by North Korea for the first time since 2017 was probably just awaiting political approval. He said such a "dangerous" act would represent "a grave escalation that would seriously threaten regional and international stability and security."