North Korea may have put fake versions of a new missile on display at a major military parade this year, UN sanctions experts said in a report.

And the allegedly mock-up missiles are not the only part of the military pomp in Pyongyang to raise the suspicions of the experts whose report was published on Friday after being held for a month by China.

The UN experts said they would investigate the giant transporter used to carry the new missile. Japanese media has said it was of Chinese origin.

The sanctions experts also suspect that luxury Mercedes cars seen in the sidestreets were smuggled into the country.

At least six of the new KN-08 missiles were proudly shown at the giant parade on April 15 to mark the 100th birthday of the North's late founder Kim Il-Sung.

"Alongside the already known missiles -- commonly identified as KN-02, Hwasongs, Nodong and Musudan -- the Democratic People's Republic of Korea paraded a new road mobile missile, called KN-08 by analysts, much larger than its other missiles," said the UN experts report.

"Missile analysts express varying levels of doubts on the operational status of the Musudan and newest KN-08, neither of which has yet been flight-tested. Analysts debate whether the KN-08s on display may have been mock-ups," said the report.

Markus Schiller and Robert H. Schmucker, of Schmucker Technologie, have also cast doubt on the missiles.

"A closer look reveals that all of the presented missiles are mock-ups," they wrote in a report carried recently on the armscontrolwonk.com website.

"There is still no evidence that North Korea actually has a functional inter-continental ballistic missile," they said.

The eight-axle transporter-launcher carrying the missiles also surprised foreign analysts. North Korea "has not previously demonstrated its capacity to build such a vehicle. The panel will further examine this," said the UN report.

The United States said last week it had raised concerns to China, after Japan's Asahi Shimbun newspaper said China shipped the transporters to North Korea. China denied the media report.

Two 'customised Mercedes Benz limousines' were also shown at the Pyongyang parade. North Korea is banned from importing such luxury items under sanctions imposed over its nuclear tests in 2006 and 2009, which the experts monitor.

The UN report said the vehicles appeared to be similar to the latest Mercedes S-class S600 series.

"A journalist has told the panel that he observed more than 10 Mercedes Benz E-class E350 series cars in front of a Pyongyang gymnasium on 16 April. The panel intends to collect more information on these vehicles," the experts said.

While the experts said they had no new indications of 'violations' involving nuclear, weapons of mass-destruction-related or ballistic missile items, the North is still defying international sanctions.

UN resolutions have not made North Korea halt its banned activities, but "they appear to have slowed them and made illicit transactions significantly more difficult and expensive."

The panel added that the North's 'difficulties in meeting its foreign exchange needs through legal exports may tempt it to expand illicit exports'.

The panel is investigating indications that an already reported illicit arms trade involved a shipment intended for Syria.

The 2007 shipment of propellant usable for Scud missiles and other items that could be used for ballistic missiles had a Syria connection, the report said. The shipment was transported through China.

The experts said they were also looking at the possibility North Korea has a deal with Myanmar on conventional weapons cooperation.