TAIPEI - Taiwan's detained former president Chen Shui-bian has written a letter to his rival and successor asking that his daughter be allowed to leave the island to study, a legislator said Monday.

Chen Hsing-yu, who admitted lying to prosecutors over the wide-ranging case that has seen her father hauled before the courts and detained for the last six months, was barred from leaving Taiwan last week to study in the United States.

A 33-year-old dentist, Chen Hsing-yu was earlier this month named a defendant in the graft case that has also dragged in the former president's wife and other family members.

Ex-president Chen has said the multitude of accusations against him and his family are politically motivated at the behest of current president Ma Ying-jeou, claims Ma has strenuously denied.

Tsai Huang-lang, of the main opposition Democratic Progressive Party (DPP), confirmed that one-time DPP leader Chen had written to Ma pleading that his daughter be allowed to leave Taiwan.

"Chen was in a bad mood. He was very much worried about his daughter Chen Hsing-yu," Tsai said after visiting the former president at the detention centre outside Taipei where Chen has been in custody since December.

Chen told Ma in his letter that the accusations against him should have no bearing on his daughter, Tsai said, although Ma's office Monday said it had received no such letter, while the travel ban remains in place.

Chiang Chih-ming, an aide to the former president, said Chen feared his daughter may even commit suicide. The former president, who left office last year after the maximum eight years allowed by the island's constitution, is accused of embezzlement, money laundering, accepting bribes on a land deal, influence peddling and forgery.

His wife, son, daughter-in-law and brother-in-law have already been charged with various offences in connection with the case, which has captivated Taiwan for months.

The ex-president has admitted misusing special expenses but says this is something which all Taiwanese politicians do and denied all the other accusations against him.