BANGKOK (AFP) - A controversial media mogul who founded Thailand's royalist "Yellow Shirt" street movement was jailed Thursday after an appeal court refused him bail over a 20-year sentence for corporate fraud, his lawyer said.

Sondhi Limthongkul, who led protests which helped trigger a 2006 army coup that toppled then premier Thaksin Shinawatra and plunged Thailand into a near-decade of political turmoil, was sentenced in 2012 but freed on bail.

On Thursday the Appeal Court upheld his conviction and refused him bail after his lawyer asked for a Supreme Court adjudication.

His conviction is for violating the Securities and Exchange Act in a case dating back to the mid-1990s.

The charismatic tycoon has faced a slew of convictions and other legal challenges, many connected to his prominent role in Thailand's febrile politics - but it is the first time he will spend a night in jail.

He was sentenced two years ago for falsifying documents used as collateral for a loan of almost 1.1 billion baht (S$45 million) for his ASTV/Manager media empire.

"Sondhi is in jail now. It is the first time that he is in jail," his lawyer Suwat Apaipakdi told AFP.

"Those who wanted to see Sondhi in jail can now be happy," added Suwat, saying he will ask the Supreme Court on Friday to re-instate bail.

Mass protests by the Yellow Shirts, formally known as the People's Alliance for Democracy, helped spur the 2006 coup by royalist generals who ousted telecoms billionaire Thaksin, then seen as Sondhi's arch-enemy.

While Thaksin fled the country to avoid jail for a corruption conviction, parties linked to his family swiftly regained their footing winning elections in 2007, powered by the Shinawatra clan's voter base in the northern part of the country.

Sondhi was among dozens of mainly Bangkok-based Yellow Shirts charged with terrorism offences over the occupation of the city's main airports in 2008 in protest at Thaksin's continuing dominance of Thai politics.

In 2010 Sondhi was also convicted of defaming Thaksin and handed a six-month suspended jail sentence.

Thailand has yet to fix the deep political fissure which followed the 2006 coup and Thaksin's self-exile.

The divided country was subject to another army coup in May this year, after months of protests against the elected government of Yingluck Shinawatra - Thaksin's younger sister.

The influence of the Yellow Shirts waned dramatically although their movement was ideologically aligned with the recent anti-Shinawatra rallies.

On Thursday Thailand's Crown Prince inaugurated a new National Legislative Assembly, replete with members appointed by the military.

The military-stacked assembly will oversee reforms leading to a new constitution which analysts say is likely to target the Shinawatra's political influence.