New satellite imagery shows North Korea has halted work at a launch pad capable of testing intercontinental missiles, possibly setting the project back by up to two years, a US website reported Tuesday.

The commercial satellite images taken on August 29 also show construction postponed on crucial fuel and oxidizer buildings designed to support future tests near the new pad, the 38 North website said.

"The slowdown, barring concerted North Korean efforts to make up for lost time, could result in a 1-2 year slip in the planned completion date of the new complex," it said.

38 North, which is the website of the US-Korea Institute at Johns Hopkins School of Advanced International Studies, said the exact cause of the work stoppage was unclear, although recent heavy rains might be a factor.

The new launch pad, being built at the Tonghae Satellite Launching Ground in the northeast of the country, had been scheduled for completion around 2015.

According to the website, it was intended to conduct future tests of larger, liquid-fuelled rockets, possibly with intercontinental ranges.

Even if completion is delayed, Pyongyang still retains the option of testing longer-range rockets at the newer Sohae Satellite Launching Station in the northwest.

North Korea carried out a failed rocket launch at Sohae in April in what it said was an attempt to put a satellite into orbit.

The UN Security Council strongly condemned the exercise as breaching a ban on the testing of ballistic missile technology, and tightened sanctions.

While work on the new pad at the Tonghae site has been halted, the satellite images showed "refurbishment" underway on an existing mobile launch pad used to test long-range rockets in 2006 and 2009.

The 38 North analysis said the images showed an uncovered exhaust hole in the launch stand that is usually hidden from view.

"The diameter of the exhaust hole is similar to that used for the... launch at Sohae, indicating that the pad is intended to launch such a rocket," it said.

The website also noted that construction was moving forward on what appeared to be a new launch control centre at Tonghae.

"This is the only site in the facility where work is proceeding at a rapid pace," it said.

The North, which is believed to have enough plutonium for six to eight bombs, tested atomic weapons in October 2006 and May 2009. Both were held one to three months after missile tests.