Chen, 57, has refused solid food since early Nov 12, after judges ordered him locked up while prosecutors pursue bribery and other graft allegations against him.

He was moved from jail late on Sunday to a nearby hospital and then to a bigger medical facility the next day, after suffering from an irregular heartbeat.

On Tuesday he accepted glucose and saline injections to stabilise his deteriorating condition.

Just after 1pm local time on Wednesday TV pictures showed an ambulance carrying Chen pulling up at the entrance to Tucheng Jail outside Taipei.

Earlier, jail official Lee Ta-chu told The Associated Press that the facility dispatched staff to fetch Chen from the hospital.

'The hospital told us it will release (Chen) to us', Mr Lee said.

'We have sent staff to carry out the procedure and bring him back'. On Wednesday morning Dr Yang Chang-bin at the hospital where Chen was being treated told reporters that his condition had improved, although 'former President Chen is still refusing to eat'.

In August, Chen admitted he broke the law by not fully disclosing campaign donations he had received, after a Nationalist lawmaker alleged that Chen's son and daughter-in-law moved US$21 million (S$32 million) to Switzerland in 2007.

Prosecutors believe Chen may have amassed millions of dollars more and say they have enough evidence to hold him as they prepare a formal indictment.

They have denied that the government has interfered in the case - charges that Chen supporters have made.

Chen, an ardent supporter of Taiwan's formal independence from rival China, denies involvement with graft and said he is being persecuted by his successor, President Ma Ying-jeou, for his anti-Beijing views.

Dozens of Chen supporters have protested daily outside the prison, backing Chen's claims of innocence and demanding his release. He has not been formally indicted, but under Taiwanese law, he can be held in jail for up to four months while prosecutors pursue his case.

On Wednesday, prosecutors working on Chen's case said they will wait until the former leader's condition stabilises before they continue questioning him. -- AP