“It (the rocket) has been launched,” a ministry spokesman told AFP without elaborating further.
There was no immediate report on the success of the launch, which Pyongyang insists is a scientific mission aimed at putting a satellite in orbit.
The Yonhap news agency, citing a government source, said the rocket had been launched from the Sohae satellite launch centre at 9:51 am (0051 GMT).
The launch followed reports in the South Korean media and satellite imagery analysis by US experts that suggested the rocket had been removed from the launch pad to repair an apparent technical problem.
North Korea had originally provided a December 10-22 launch window, but extended that by a week on Monday when a “technical deficiency” was discovered in the first-stage control engine.
North Korea last attempted to launch its three-stage Unha-3 carrier in April, but the rocket exploded shortly after take-off.
A successful launch this time would mark a major advance in the North’s bid to mate an intercontinental ballistic missile (ICBM) capability with its nuclear weapons programme.
Washington and its allies insist the launch is a disguised ballistic missile test that violates UN resolutions triggered by Pyongyang’s two nuclear tests in 2006 and 2009.
In 2006 the Security Council imposed an embargo on arms and material for ballistic missiles and weapons of mass destruction. It also banned exports of luxury goods and named individuals and companies to be subject to a global assets freeze and travel ban.
In 2009, it imposed a ban on North Korea’s weapons exports and ordered all countries to search suspect shipments.