North Korea is replacing a faulty section of a long-range rocket in a bid to put its launch schedule back on track, and is receiving help from Iranian missile experts, a South Korean newspaper reported Monday.

North Korea had said Sunday it was considering delaying the launch -- slated for some time between December 10-22 -- because of unspecified "problems" uncovered by technicians at its Sohae satellite launch station.

But the Chosun Ilbo newspaper on Monday cited new satellite images that suggested the faulty component was being replaced to allow the launch to go ahead.

"A new third stage of the North's three-stage missile Unha-3 was seen being moved Saturday afternoon from a missile plant... towards the launch site," the newspaper quoted an unidentified government source as saying.

The South's Yonhap news agency quoted a separate government source as saying a component was being moved but that it was unclear what kind.

"We have yet to analyse information that it is a third stage of the rocket or other parts," the Yonhap source said.

North Korea says the rocket launch is a peaceful mission aimed at putting a satellite in orbit.

The United States and its allies view it as a disguised ballistic missile test banned under UN resolutions prompted by the North's nuclear tests in 2006 and 2009.

In a separate report Monday, the Chosun Ilbo -- known for its comprehensive North Korean coverage -- said a group of Iranian missile experts was in North Korea offering technical assistance for the planned launch.

The Iranians were invited after Pyongyang's last rocket launch in April ended in failure, the newspaper said, citing a Seoul government official.

"A car seen at the... launch site has been spotted driving back and forth from the accommodation facility nearby. It is believed to be carrying Iranian experts," the official said.

Earlier this month, Japan's Kyodo news agency quoted a western diplomatic source as saying Iran had stationed defence personnel in North Korea since October to strengthen cooperation in missile and nuclear development.

North Korea and Iran are both subject to international sanctions over their nuclear activities and their governments share a deep hostility towards the United States.

Leaked US diplomatic cables in 2010 showed that US officials believe Iran has acquired ballistic missile parts from North Korea. A 2011 UN sanctions report said the two countries were suspected of sharing ballistic missile technology.

On Sunday, the North's Korean Committee of Space Technology said its scientists were "seriously examining the issue of readjusting the launching time of the satellite for some reasons."

The committee gave no further details, but analysts suggested potential technical troubles. A US think-tank, the US-Korea Institute at Johns Hopkins University, said Friday that preparations may have been delayed by heavy snow.

Some analysts said the new leader, Kim Jong-Un, may have been rushing the event to mark the first anniversary of the death of his father and former leader Kim Jong-Il on December 17.