Seoul: North Koreans set piles of old bills alight this week in anger over their government's surprise move to redenominate the national currency, a report said, a sign of growing frustration among citizens left with hoards of worthless bills.

On Monday, the communist government informed citizens and foreign embassies that it would redenominate the national currency, the won. But it limited the maximum amount of old bills that could be converted into new ones, telling residents to deposit the rest in government-run banks, according to media reports and diplomats.

There are widespread doubts among North Koreans whether they would be able to get their money back, they said.

Angry citizens burned piles of old bills at two separate locations in the eastern coastal city of Hamhung on Monday, the Daily NK, a Seoul-based online news outlet that focuses on North Korean affairs, reported late Thursday, citing an unidentified North Korean resident.

It quoted the resident as saying he saw graffiti and leaflets criticizing North Korean leader Kim Jong Il in and around a college in Hamhung - a rare move in a country where the totalitarian government keeps tight control over its 24 million people.

North Korea announced that the exchange rate would be set at 100 old won to 1 new won. Initially, residents were only allowed to exchange 100,000 won per household for the new currency.

But the government later increased the amount, allowing each family member to trade an additional 50,000 old won for new ones.