North Korea has resumed construction work on a missile launch site on its northeast coast after a months-long hiatus, part of a renewed push for its nuclear and missile programmes, according to a US think-tank.

Recent satellite imagery shows work has resumed on new facilities at the North's Tonghae launch site, the US-Korea Institute of Johns Hopkins University posted on its 38 North website.

The facilities appear designed to test future generations of larger, more capable rockets, it said.

The restart of work at Tonghgae indicates that North Korea is still committed to maintaining two launch sites along with the Sohae site on the west coast.

But the institute said there were no signs of an imminent long-range rocket test at either site.

The US-Korea Institute said in October that North Korea has undertaken major construction work at Sohae, possibly to cater to larger and more mobile weapons.

The Sohae site was used for the launch in December of the North's Unha-3 carrier, which successfully placed a satellite in orbit.

Construction at Tonhae had appeared to be on hold since early 2013.

But images taken between September 16 and November 18 show work resumed on the new launch control center and the assembly building, the US-Korea Institute said.

There is no sign of further construction yet at the new launch pad or on an access road, it said.

The North's rocket launch in December was condemned by most in the international community as a disguised ballistic missile test that violated UN sanctions on Pyongyang.

North Korea insisted it was a purely scientific mission and vowed to push ahead with similar launches in the future.

North Korea is pushing for a resumption of six-party talks on its nuclear programme, but the United States says it must first demonstrate a commitment to denuclearisation.

Another long-range rocket launch would be taken as a step in the opposite direction and almost certainly result in fresh sanctions.

The US-Korea Institute said in early November that the North was making progress on an intercontinental ballistic missile capable of delivering a first-generation nuclear warhead to the continental United States.

Missile delivery has often been cited as the main weakness of the North's nuclear weapons programme which, after three tests, is believed to be close to mastering the key technology of warhead miniaturisation.