Thailand's jailed former prime minister Thaksin Shinawatra has requested a royal pardon, a government minister said Thursday.

The 74-year-old billionaire, twice elected PM and ousted in a 2006 military coup, was sent to prison last week immediately after returning to the kingdom from 15 years of self-exile.

His homecoming coincided with his Pheu Thai party returning to government in alliance with several pro-military parties, sparking widespread speculation of a deal to cut his jail time.

Caretaker justice minister Wissanu Krea-ngam said Thaksin had applied for a pardon from the eight-year jail term he is serving for convictions for graft and abuse of power. "We have received (the request), the rest will be according to the procedure," Wissanu told reporters.

Asked how long the process would take, Wissanu said: "It is purely based on royal grace. The procedure from the government is not long, but it depends on the length of (the king's) consideration."

Under Thai law, prisoners can submit a pardon application that is passed from the justice minister through the prime minister to the privy council before going to King Maha Vajiralongkorn.

Officials say the process takes one to two months, if all the paperwork is in order.

On landing in Bangkok last week, Thaksin's first public act was to prostrate himself in homage before a portrait of the king at the airport.

Divisive figure

Thaksin is one of the most influential but divisive figures in modern Thai history.

Loved by millions of rural Thais for his populist policies in the early 2000s, he is reviled by the country's royalist and pro-military establishment, which has spent much of the past two decades trying to keep him and his allies out of power.

Hours after Thaksin landed in Bangkok to a hero's welcome from hundreds of supporters, Pheu Thai's Srettha Thavisin was confirmed as prime minister on Tuesday -- the party's first premier since Thaksin's sister Yingluck was thrown out in a coup in 2014.

Just hours after being sent to jail, Thaksin was moved to a police hospital, with prison medical officers saying he needed close monitoring for various health problems, including heart trouble.

Thai media reported that Thaksin had been installed in a private VIP suite on the 14th floor of the Police General Hospital in downtown Bangkok.

A small anti-Thaksin group gathered in Bangkok Thursday afternoon to demand he serve his time.

Before last week Thaksin had not set foot in the kingdom since 2008, living mostly in Dubai to avoid criminal cases he long maintained were politically motivated.

But earlier this year he said he was willing to face justice in order to return home and see his grandchildren.

New PM Srettha heads a controversial coalition that includes parties linked to the coup-maker generals who ousted Thaksin and Yingluck.

The alliance shuts out the progressive Move Forward Party (MFP), which rode a wave of youth and urban discontent at nearly a decade of military-backed rule to win most seats in the May election.

But MFP's reformist push to amend royal defamation laws and tackle business monopolies spooked the kingdom's powerful elite, and the party's leader Pita Limjaroenrat was blocked from becoming prime minister. (AFP)