U.S. Deputy Secretary of State Tony Blinken stressed during his trip to Japan over the weekend that North Korea's nuclear test "demands a response beyond business as usual," the State Department said Monday.

While in Tokyo from Jan. 15-17, the No. 2 American diplomat held bilateral and trilateral meetings with his South Korean and Japanese counterparts mainly to discuss strategies to punish North Korea for its fourth nuclear test earlier this month.

The three countries discussed "our unified response to North Korea's recent nuclear test, a flaunting of that country's international obligations and a threat to regional stability," the department said in a readout.

"All parties affirmed our mutual interest in securing a robust international response to uphold a rules-based order and to promote norms that safeguard the stability of the region," the department said. "The deputy secretary stressed that such destabilizing activity demands a response beyond business as usual."

Blinken also commended the South Korean and Japanese governments for "their courageous statecraft in coming to a historic agreement on the sensitive 'comfort women issue and offered the United States' full support for its implementation," the department said.

Seoul and Tokyo reached a landmark agreement on the issue of Japan's wartime sexual slavery, removing the biggest thorn in relations between the two countries and offering hope for significant progress in U.S. efforts to forge stronger security cooperation with the two allies in a region marked by a rising China.

Blinken is scheduled to visit Seoul on Monday for further discussions on North Korea.

After Seoul, he plans to visit China to press Beijing for cooperation in adopting a strong U.N. Security Council resolution on the nuclear test. China, the North's last-remaining major ally, has shown a lukewarm attitude about calls for punishing Pyongyang.

Secretary of State John Kerry also plans to visit Beijing later this month.

Chinese cooperation is key to adopting a Security Council resolution because it is one of the five veto-holding members of the council, along with Britain, France, Russia and the U.S. (Yonhap)