Taipei - Four Taiwan prosecutors flew to Singapore Wednesday to seek the city-state's help in investigating suspected money laundering by former president Chen Shui-bian.

The prosecutors want to check a bank account of Wu Ching-mao, brother of Chen's wife, Wu Shu-chen, because she had allegedly wired some of Chen's campaign funds to the account.

Singapore has told Taiwan that it is willing to offer legal assistance because Singapore does not allow foreigners to use its financial system to conduct illegal activities, Taiwan's Central News Agency said.

Allegations of money laundering by Chen surfaced in June when Swiss judicial authorities alerted Taiwan that they found a remittance into the bank account of Chen's daughter-in-law, Huang Jui-ching, suspicious.

On August 14, Chen admitted that Wu Shu-chen had remitted 21 million US dollars - campaign funds from the 2000 and 2004 presidential election that Chen had not declared - into several foreign bank accounts and eventually into a Swiss bank account.

Prosecutors have barred Chen; Wu Shu-chen; Wu Ching-mao; Chen's son, Chen Chih-chung; and Huang Jui-ching from leaving Taiwan.

Taiwan has also acquired legal assistance from Switzerland.

In Taipei, prosecutors continued to investigate how much money was amassed illegally, how much was wired into overseas bank accounts and how many people were involved in the alleged money laundering.

Chen's financial scandal has further tarnished the image of the Democratic Progressive Party (DPP). Chen quit the party on August 15 as the party, embarrassed by Chen's scandal, was preparing to expel him.

On Wednesday, an opinion poll published by the United Daily News showed that support for the DPP has fallen from 51 per cent when Chen became president, to 33 per cent when he won a second term in 2004, to the current 11 per cent.

Discontent with the DPP has risen from 21 per cent in 2000, 51 per cent in 2004 to a current 73 per cent, according to the poll of 981 adults.

Chen, former DPP chairman, served as Taiwan's president from 2000 to 2008.

Corruption scandals involving Chen's family and DPP officials caused the party to lose the 2008 election to the pro-China Chinese Nationalist Party. (dpa)