"North Korea should refrain from actions that aggravate tensions and focus on denuclearization talks and the implementation of its commitments from the September 19, 2005 joint statement," said State Department spokesman Karl Duckworth.

"This type of North Korean behavior is not helpful," he told AFP after North Korea test-fired seven missiles off its east coast earlier Saturday, according to South Korean officials.

The ballistic missiles -- which the North is banned from firing under UN resolutions -- were launched into the Sea of Japan.

It was the biggest salvo of ballistic weaponry since the North fired a long-range Taepodong-2 and six smaller missiles on US Independence Day in 2006.

Under the 2005 agreement, North Korea promised to give up its nuclear program in exchange for a US pledge not to attack or invade it and to work toward normalized relations.

The United States and other parties to the agreement -- China, Japan, Russia, and South Korea -- also offered to put together an energy package for North Korea.

But North Korea announced last April that it was walking out of the six-party talks and resuming operation of its nuclear facilities.

Pyongyang conducted its second nuclear test in May.

"What North Korea needs to do is fulfill its international obligations and commitments," Duckworth said, adding that North Korean missile launches "highlight the importance of fully implementing the provisions of the UN resolutions."

Professor Kim Yong-Hyun of Seoul's Dongguk University said the launches were clearly timed to coincide with US Independence Day.

"This is a thinly veiled warning to the United States and the international community that it may launch long-range missiles next time," he told AFP.

A US delegation met this week with Chinese officials for talks on implementing UN sanctions imposed on North Korea in retaliation for its most recent nuclear test.

Delegation head Philip Goldberg -- the State Department's point man on coordinating implementation of the sanctions -- told reporters on Thursday he had "very good discussions" in Beijing.

"Our objective is the full implementation of the UN resolutions on North Korea," he said.

"We intend to implement these resolutions with the overall goal of returning to a path of denuclearisation and nonproliferation on the Korean peninsula."

US embassy spokesman Richard Buangan said Goldberg met with officials from China's foreign ministry.

China, which supported the resolution, has been criticised by the United States in the past for lacking enthusiasm for implementing UN sanctions against North Korea, its neighbour and ally.