North Korean leaders claim to have successfully tested a new intercontinental ballistic rocket engine.

The technology would give it the ability to stage nuclear strikes on the US.

The engine's ground test would be a big step forward for the North's nuclear weapons programme.

However, the North may still need a good deal of work before it can hit the US mainland with nuclear missiles.

South Korean officials say North Korea does not yet have a reliable intercontinental ballistic missile, let alone the ability to arm it with a nuclear warhead.