North Korea said Saturday it would hold an annual parliamentary session next month around the time of a planned rocket launch by the nuclear-armed state that has sparked widespread condemnation.

The meeting of the rubber-stamp body will also take place just two days before deceased founder Kim Il-Sung's 100th birthday and will be the first under new leader Kim Jong-Un.

Pyongyang's official Korean Central News Agency (KCNA) said the Supreme People's Assembly (SPA) would convene on April 13.

The assembly is constitutionally able to appoint the chairman of the National Defence Commission (NDC), a top military decision-making body wielding great influence over the highly militarised communist state.

The parliament will likely promote Jong-Un, currently vice chairman of the commission, to the NDC's highest post, which was held by his father and the country's ex-leader Kim Jong-Il, who died in December from a heart attack, analysts said.

Separately, the North's ruling communist party said last month it would convene a rare special conference in April on an unspecified date in an apparent attempt to wrap up the power transfer to the new leader.

The party meeting is likely to appoint Jong-Un to his father's old posts of party general secretary and chief of its Central Military Commission, analysts said.

Jong-Un has been proclaimed the "great successor" but has so far been formally appointed to only one of the late Kim's posts, commander-in-chief of the 1.2 million-strong military.

North Korea announced earlier this month it would launch a rocket between April 12-16 to put a satellite into orbit to celebrate the centenary of Kim Il-Sung's birth.

The move has been condemned by the United States, South Korea and other nations as a pretext for a long-range missile test banned by the UN.

It has also jeopardised a deal with the United States announced last month on suspending uranium enrichment and long-range missile tests in return for food aid.

A senior US official warned that the rocket launch would be aimed south for the first time and impact in an area "roughly between Australia, Indonesia and the Philippines".

Kurt Campbell, the assistant secretary of state for East Asian and Pacific affairs, delivered the message in person to Australian Foreign Minister Bob Carr, the Sydney Morning Herald reported Saturday.

"We have never seen this trajectory before," he was quoted as saying.

Philippine Foreign Department spokesman Raul Hernandez told AFP that his country's military was coordinating with the US military to track the path of the planned launch.

Indonesia's deputy foreign minister said his country was "concerned" by North Korea's plans.

On Friday, the North said preparations "have entered a full-fledged stage of action" and promised unspecified "counter-measures" against opponents of the operation.

It came shortly after Tokyo said it was preparing missile defences to shoot down the rocket if it threatened Japan. North Korea's main ally China called for all sides to "keep calm and exercise restraint".

Professor Yang Moo-Jin of the University of North Korean Studies in Seoul said that "the rocket launch and parliamentary and party meetings are all part of the North's plan to usher in a new era under Jong-Un."

"It will declare it has become 'a strong and prosperous state' on the 100th anniversary," he said.

Cheong Seong-Chang of the Sejong Institute said the North was likely to name Kim Jong-Il the eternal chairman of the NDC in the same manner that its founder Kim Il-Sung was declared the country's president for eternity.

"The North's parliament may change the constitution to create a new state organ to replace the NDC and make Jong-Il the eternal NDC chairman," Cheong told AFP.

World leaders including US President Barack Obama are meeting in Seoul from Monday for a summit officially focused on nuclear terrorism.

On Saturday UN chief Ban Ki-moon and South Korean President Lee Myung-Bak described the planned launch as a "grave provocative act against the international community" in a joint statement released by Lee's office.

They said that North Korea's announced plan was "in breach of a UN Security Council resolutions" and vowed to tackle together any threats arising from it.