Former Taiwan "president" Chen Shui-bian said yesterday he had done nothing wrong after a prosecutor questioned him for more than four hours about a bribery case involving his family.

The family is suspected of depositing at least T$1 billion ($31.7 million) in banks in Japan, the United States, the Cayman Islands, Singapore and Switzerland, among other places, Taiwan media reported citing the Supreme Court prosecutor's office.

Chen, in office from 2000 to May 2008, denies any wrongdoing.

"There is absolutely no graft, absolutely no stolen money," he told a news conference.

He said expenses exceeded revenues of about T$200 million in the "state affairs" fund, and that no money was laundered overseas.

"You can check it out," Chen said.

A lawyer by profession, Chen had made a push for the island's independence when in office.

A special Supreme Court prosecutor questioned Chen yesterday morning until he complained of feeling unwell, a spokesman told reporters.

The spokesman would not give details of the questioning, the third such session since Chen left office on May 20 after eight years in power.

Investigations into the affairs Chen and his family have tarnished the image of his Democratic Progressive Party, which faces local elections next year.

Chen has admitted "expatriating" $20 million, but claims the money came from unused campaign contributions - permissible under Taiwan's law at the time - and was intended to underwrite the island's "diplomatic work".

Chen and his wife, Wu Shu-chen, left the party on Aug 15.