Seoul, Mar 27: North Korea on Thursday expelled South Koreans from a joint factory park north of the border in retaliation for the new government's tough tone towards Pyongyang, a move Seoul warned could chill once warming ties.

The predawn expulsion of the officials at the Kaesong industrial site, once hailed as a model of economic cooperation, is one of the most aggressive moves in years by the destitute North against its wealthy neighbour that supplies it with aid.

Presidential Blue House Spokesman Lee Dong-kwan said after an emergency meeting that the North's measure "was a very regrettable incident that could damage progress of economic cooperation between the South and the North".

President Lee Myung-bak's government, in office barely a month, has pushed the touchy North to clean up its human rights record, repatriate its citizens held by the communist state and make progress on nuclear disarmament.

Spokesman Lee said North Korea needs to be more predictable in its dealing with the South, adding his government did not want the situation to deteriorate.

Park Young-ho, an expert on the North at the South's Korea Institute for National Unification, said: "You can see this move as North Korea trying to train the new South Korean government and put pressure on it."

He added Pyongyang was also looking to stir up conflict in the South over how to treat its prickly neighbour.

The North's official media has yet to report that Lee has become president, the first conservative in the job after a decade of left-of-centre leaders who handed over billions of dollars in aid to try to win over the reclusive state and maintain stability on the peninsula.