Family members of Chen, who was in office from 2000 to May 2008, were suspected of graft, prompting prosecutors to investigate them over the past few years, tarnishing the image of the Democratic Progressive Party.

Merrill Lynch sent two Asia-based executives to Taipei on Monday to clarify the company's role in the case, the Chinese-language China Times paper said.

'Merrill Lynch told us they are willing to cooperate with us,' prosecutor Chu Chao-liang told Reuters by phone.

'Within legal procedures, they would be willing to provide information,' Mr Chu said, referring to bank accounts of Mr Chen's family members. He declined to elaborate further.

Ms Vicki Kwong, a Merrill Lynch spokesman, declined to comment on any aspects of the case or whether any company executives had arrived in Taiwan.

Taiwan's Justice Ministry said earlier this month its Swiss counterparts have requested assistance in an investigation into the money laundering involving accounts held by Mr Chen's son Chen Chih-chung and daughter-in-law Huang Jui-ching.

Swiss authorities have frozen US$21 million (S$29.9 million) in two accounts Mr Chen and Ms Huang they had previously set up with Merrill Lynch and Royal Bank of Scotland, Taiwan prosecutors have said. -- REUTERS