Thailand's former prime minister Thaksin Shinawatra (center) arrives at Don Muang airport in Bangkok, Thailand, on Aug 22, 2023. (PHOTO / AP)

BANGKOK - Thailand's former prime minister Thaksin Shinawatra was hospitalized on his first night in prison after his historic return from self-exile, officials said on Wednesday, citing concern about his heart and blood pressure.

The influential founder of Thailand's populist Pheu Thai Party was transferred to a police hospital overnight, 15 hours after homecoming.

The Corrections Department said Thaksin Shinawatra was transferred in the early hours of Wednesday after being unable to sleep and experiencing chest tightness and high blood pressure on his first night in prison

The Corrections Department said the 74-year-old Thaksin was transferred in the early hours of Wednesday after being unable to sleep and experiencing chest tightness and high blood pressure on his first night in prison.

"Physicians agreed that to prevent dangerous risks to his life, he be transferred to the police hospital," it said.

Soponrat Singhajaru, a senior doctor, confirmed his condition had improved since he was admitted. A representative for Thaksin declined to comment.

Thaskin was ousted in a 2006 military coup and was in self-exile two years later when he was sentenced to jail for graft and abuse of power.

His hospitalization is the latest twist in chaotic few months in Thai politics that saw the progressive Move Forward party triumph in a May election then end up in opposition, and the populist heavyweight Pheu Thai, twice toppled by the military, agree to form a government with army-backed parties.

READ MORE: Thai ex-PM Thaksin to return from exile Tuesday, daughter says

Thaksin returned on a private jet to cheering crowds on Tuesday before being escorted to a court then to a jail, in dramatic scenes that stole the spotlight from fellow tycoon Srettha Thavisin, who was chosen as prime minister hours later.

The unimpeded return of Thaksin and Srettha's surprisingly smooth ascent to the top job will add to speculation that Thaksin had struck a deal with longtime enemies in the military and conservative establishment for his safe return and, possibly, an early release from jail.

Thaksin and Pheu Thai have denied that.

Srettha, a US-educated property mogul, has been endorsed as premier by the king and is expected to form an 11-party coalition in days ahead. Election winner Move Forward declined to back Srettha, calling his alliance with unpopular pro-military parties a betrayal of the will of the people.

News of Thaksin's struggle on his first night in prison drew mixed reactions on social media.

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The hospital said there was no special treatment and it admitted prisoners regularly.