Pyongyang has recalled its ambassador to Vietnam as an act of protest against the country for its role in the recent mass-defection of North Koreans to the South.

According to diplomatic sources in Beijing, North Korea has demanded an apology from Hanoi for apparently cooperating with Seoul in helping the defectors escape to South Korea.

The North has also demanded that Vietnamese authorities pledge not to take part in similar operations in the future, and threatened to remove all embassy staff from the Southeast Asian country if Hanoi did not adhere to such a promise.

Pyongyang's move is being seen as a warning to other third countries that it intends to take strong measures if similar events take place in the future.

Nearly 500 North Koreans flew to Seoul last month via Vietnam in the single largest such defection.