Thailand's former leader Thaksin Shinawatra was moved to a police hospital overnight after feeling unwell on his first night in jail Wednesday.

"The prison asked doctors and nurses to diagnose him and they recommended referring the case to the police hospital for the safety of the prisoner," Ayuth Sintoppant, the director general of Department of Corrections told the Reuters news agency.

Sintoppant said he was accompanied by eight prison guards when he was transferred at night.

Reuters reported that Thaksin developed high blood pressure and was not able to sleep.

A prisons department statement said the former leader, who is 74-years-old, suffered "chest pressure." The statement added the biggest concern was his heart.

Thaksin has pre-existing issues with his heart, lungs, spine, and blood, officials from the Department of Corrections said.

Thaksin's return coincides with vote to select new PM

The former prime minister was sentenced to jail for eight years on corruption charges immediately upon his return to the country after more than 15 years of self-imposed exile.

His return after that many years coincided with a parliamentary vote for a new prime minister, with lawmakers hoping to break a political deadlock after elections in May.

Hours later, Srettha Thavisin of the Pheu Thai party, which was founded by Thaksin, secured enough votes to become prime minister, ending months of legal wrangling.

The progressive Move Forward Party won the most votes in May elections but was blocked from taking power by conservative senators.

rm/jsi (Reuters, AFP)