The US ambassador to the United Nations, Susan Rice, said Monday that if North Korea goes ahead with a planned rocket launch, the UN Security Council will likely convene to discuss the issue.

Rice told CNN that either a rocket launch or an eventual nuclear test, which a South Korean official warned could follow, would be a "blatant violation" of North Korea's obligations under past UN Security Council resolutions.

She cautioned that if North Korea were to "move beyond such a provocative step as a missile launch to a nuclear test, obviously their isolation will only increase."

"In New York, I anticipate the Council would convene to discuss this and to respond in a credible fashion, both to the missile launch and to any potential additional subsequent actions," Rice said.

The United States and other nations said the satellite launch -- scheduled to take place between April 12 and 16 -- will be a pretext for a ballistic missile test, in defiance of UN resolutions and a US-North Korean deal.

A South Korean official said the North appeared to be preparing to follow up the launch with a third nuclear weapons test.

But North Korea says the launch was planned to mark the 100th anniversary of the birth of founding president Kim Il-Sung, and rejected suggestions it was a disguised missile test.

"We are not doing it for provocative purposes," Jang Myong-Jin, head of North Korea's Tongchang-ri space centre in the far northwest, told journalists Sunday.

S. Korea, US defence chiefs discuss N. Korea rocket
Seoul (AFP) April 10, 2012 - South Korean and US defence chiefs vowed Tuesday to take coordinated action in the face of North Korea's planned rocket launch, calling it "a grave provocation", the defence ministry said.

Defence Minister Kim Kwan-Jin and US Defence Secretary Leon Panetta agreed in their telephone conversation to forge close cooperation against the launch and maintain a strong defence posture, the ministry said.

"Both ministers shared the view that North Korea's long-range missile launch is a grave provocation," it said in a statement without disclosing what action was envisaged.

The poor but nuclear-armed North attracted international condemnation after it announced a plan to launch a satellite sometime from April 12 to 16, to mark the centenary of the birth of late founding president Kim Il-Sung.

Pyongyang insists the launch is a peaceful space project but the United States and South Korea view it as a disguised missile test in breach of UN resolutions.

South Korea has vowed to shoot down the rocket if it strays into its territory. Japan has said it may do likewise.

The South's military plans to deploy destroyers armed with missiles to the Yellow Sea to track the rocket.

The transport ministry said it would provide up-to-date information to shipping on the rocket launch.

All 15 maritime traffic control centres will be placed on alert from Wednesday, issuing navigation warnings every two hours to protect vessels operating in the Yellow Sea, it said.

The first stage of the rocket is expected to fall in waters 170 kilometres (100 miles) west of Gunsan in the southwest of South Korea, it said.