S.Korea says North 'rocket' could fly 10,000km

North Korea's recent rocket launch amounted to the test of a ballistic missile capable of carrying a half-tonne payload over 10,000 kilometres, the South Korean defence ministry said Sunday.

North Korea launched its three-stage Unha-3 rocket on December 12, insisting it was a purely scientific mission aimed at putting a polar-orbiting satellite in space.

Sunday's estimate was based on analysis of an oxidizer container -- recovered from the rocket's first-stage splashdown site -- which stored red fuming nitric acid to fuel the first-stage propellant.

"Based on our analysis and simulation, the missile is capable of flying more than 10,000 kilometres with a warhead of 500-600 kilograms," a defence ministry official told reporters.

Without any debris from the second and third stages to analyse, the official said it could not be determined if the rocket had re-entry capability -- a key element of inter-continental ballistic missile (ICBM) technology.

Most of the world saw the North's rocket launch as a disguised ballistic missile test that violates UN resolutions imposed after Pyongyang conducted nuclear tests in 2006 and 2009.

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.

The debris collected by the South Koreans was made of an alloy of aluminium and magnesium with eight panels welded manually.

"Welding was crude, done manually," the ministry official said, adding that oxidiser containers for storing toxic chemicals are rarely used by countries with advanced space technology.