SEOUL - North Korean troops are under orders to shoot unauthorized border-crossers to prevent mass defections following a shock currency revaluation which wiped out savings, a report said Monday.

South Korea's Chosun Ilbo newspaper said the orders were given to forestall any mass flight to China by middle-class North Koreans who had seen their assets vanish.

"We don't have any information that there will be a riot or a mass defection, but since North Koreans have never so far taken collective action, they are more likely to choose defection if the situation worsens," it quoted an unidentified Seoul intelligence official as saying.

South Korea's unification ministry declined to comment on the report ? the latest in a series speaking of public anger and frustration in the hardline communist state.

The changeover to a new currency ended Sunday but public discontent and confusion remain unabated, Seoul-based Internet newspaper DailyNK said.

Citizens could exchange old won banknotes for new ones at the rate of 100 to one. But restrictions were imposed on the total sum that could be swapped, leading many to fear the loss of their savings.

Chosun said security authorities have gone on emergency alert after old bills carrying the image of late president Kim Il-Sung were found torn or damaged on piles of garbage in several cities.

Graffiti and leaflets criticizing current leader Kim Jong-Il have also started to appear, it said.

Analysts say the revaluation is aimed at clamping down on the fledgling free-market economy and tightening the regime's grip.

A North Korean central bank official has himself been quoted as saying the aim is to weaken the role of free markets and strengthen the socialist system.

Jo Song-Hyon, quoted by Japan-based pro-Pyongyang newspaper Choson Sinbo last week, said the North would further strengthen "socialist principles and order in economic management".

Jo said more steps would be taken to stop disorder.

The regime in recent years has clamped down on street markets that sprang up after the national food distribution system collapsed during famines in the 1990s.

Authorities have launched a major publicity campaign to justify the shock move, the DailyNK said.

Vehicles with loudspeakers are being used to justify the changes as "great socialist reforms" for workers and peasants, it quoted informants in the North as saying.

The North was also using its internal broadcasting network for an all-out publicity campaign, saying the revaluation "heralds the start of a powerful socialist nation".

DailyNK said authorities changed their policy several times in the face of public anger. After initially limiting the total which can be changed to 100,000 won (around 30-50 dollars at black market rates), the limit had been raised to 300,000 won for a family of four.

The remaining old currency could be deposited in banks but reports say citizens can be barred from accessing their savings.