North Korea has extended the launch period for its planned rocket launch by one week, citing technical problems.
The Korean Committee of Space Technology said in a statement carried by the official Korean Central News Agency on Monday that the rocket would kick off on December 29 due to "technical deficiency" in a rocket engine module.
The statement did not elaborate but said technicians were "pushing forward" with final preparations for the launch.
The North had originally set up a 13-day launch window, starting on Monday.
A South Korean newspaper quoted a government source as saying on Monday that North Koreans were replacing the faulty section of the rocket with the help from Iranian missile experts.
The Chosun Ilbo newspaper 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 on Saturday afternoon from a missile plant... towards the launch site," the newspaper said.
"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 told the newspaper.
The Iranians were invited after Pyongyang's last rocket launch in April ended in failure, the newspaper 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 co-operation 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 US.
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.
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.