South Korea has recovered what it believes to be debris from the engine of the long-range rocket launched by North Korea this month, the defence ministry said Friday.

"If it is confirmed to be engine debris, it will be very useful for analyzing North Korea's missile technology," a ministry spokesman said.

He said navy ships had retrieved six chunks of debris from the rocket that was launched -- to international condemnation -- on December 12.

Pyongyang said the launch was a purely scientific mission aimed at placing a polar-orbiting earth observation satellite in space.

Most of the world saw it as a disguised ballistic missile test that violated UN resolutions imposed after the North's nuclear tests in 2006 and 2009.

Two days after the launch, the South recovered an oxidiser container, which had stored red fuming nitric acid to fuel the first-stage propellant.

After studying the oxidiser tank, military experts said the rocket launch amounted to the test of a ballistic missile capable of carrying a half-tonne payload up to 10,000 kilometres (6,200 miles).

The success of the launch was seen as a major strategic step forward for the isolated North, although missile experts differed on the level of ballistic capability demonstrated by the rocket.