UNITED NATIONS, United States (AFP) - A North Korean ambassador said in New York on Tuesday that Pyongyang might launch a new missile test in October.

Any rocket launch would almost certainly be viewed by the international community as a disguised ballistic missile test and result in the imposition of fresh sanctions.

Asked about reports of a possible missile test in October, the ambassador said Oct 10 marks the 70th anniversary of the founding of the North's ruling Workers' Party.

"I'm sure that we will have a great, grand celebration," Jang Il Han told a rare press conference, convened at North Korea's permanent mission to the United Nations.

Jang, who is tasked with relations with the United States, said North Korea was "free to do whatever we want."

"We stated in the past that we will respond to the military deterrence and pressure of the United States with modernisation and expansion and strengthening of our nuclear forces.

"So I'll not rule out any possibility of doing one of these things but... I'm not in a position to say with confidence it will happen," he added.

Last week, South Korea's Yonhap news agency cited "credible intelligence" that North Korean leader Kim Jong-Un had ordered the launch of a satellite to mark the party's 70th anniversary.

According to an unnamed government source, North Korea has completed work on an extended 67m gantry capable of handling a rocket twice the size of the 30m Unha-3 rocket launched in December, 2012.

The Unha-3 launch was widely condemned overseas as a ballistic missile test and triggered additional UN sanctions.

North Korea is banned under UN Security Council resolutions from carrying out any launch using ballistic missile technology, although repeated small-range missile tests have gone unpunished.