The unnamed spokesman said any sanctions would be seen as an "act of hostility" and would be in defiance of the September 19 joint statement - a 2007 disarmament-for-aid deal reached between the North and the other five parties to the talks: China, Japan, Russia, South Korea and the United States.

"If the September 19 joint statement is nullified, there will be neither the foundation nor the meaning for the existence of the six-party talks," the spokesman said.

Journalists held

The North Korean warning comes amid increased pressure on Pyongyang to release two American journalists currently detained in the country.

Reporters without Borders (RWB) has said that North Korea must prove Laura Ling and Euna Lee had crossed into its territory - or release them.

Pyongyang says attempts to stop the rocket launch are 'discriminatory' [Reuters]

"If they were captured on Chinese territory, that could constitute a violation of international law," Vincent Brossel, the Asia-Pacific bureau chief for RWB, told the Associated Press.

"If it is a kidnapping in Chinese territory, the Chinese government must launch an investigation against this violation of their sovereignty."

South Korean media reports have said the journalists were undergoing "intense interrogation" at a guesthouse in Pyongyang's outskirts run by North Korean military intelligence.

Some reports have said they are being accused by the North of spying, although the US state department said on Tuesday it did not believe that to be the case.

Tensions rising

Meanwhile, the impending rocket launch continues to raise tensions in the region.

South Korea's Yonhap news agency quoted Wi Sung-lac, the country's top nuclear negotiator, as saying that the country is working on responses to a rocket launch.

"As the clock ticks, we are placing more weight on countermeasures after a launch," Wi said.

Christian Le Miere, an editor at Jane's Intelligence Review, told the Associated Press that satellite images from March 16 indicate that preparations for the launch of a rocket are moving forward, but the rocket was not yet on the launch pad in the photos.

Japan has previously said it could shoot down debris from a launch, but the country's foreign minister has expressed doubts over whether that would be possible.

Hirofumi Nakasone told the Associated Press "it would be difficult" for Japan to intercept fragments of a missile that may enter Japanese territory after a launch.

North Korea has warned that attempts to deny Pyongyang the right to use space for "peaceful" purposes was discriminatory and not in keeping with the "spirit of mutual respect and equality" it says it agreed to under the six party nuclear talks.

Under the deal, the North pledged to abandon its nuclear programme in exchange for aid and security guarantees.

However, the process has been stalled since last year over a disagreement with Washington over how to verify the North's shutdown of its nuclear activities.