Thai protesters who have massed on Bangkok's streets for six months said Thursday they would appoint a new government, following the removal of Premier Yingluck Shinawatra by a court.

The announcement comes as the ailing ruling party expressed fears a new cabinet -- appointed to bolster its authority after Yingluck's dismissal -- could also be nobbled by a legal ruling.

Observers warned the protesters' move would likely enrage pro-government supporters, risking further violence as the country lurches deeper into a political crisis.

"Tomorrow (Friday) we will take steps towards appointing a new government," protest spokesman Akanat Promphan told AFP.

"After the Constitutional Court's decision yesterday we decided to move up our schedule.... the government has lost all legitimacy and any claim it has to govern the country."

It was not immediately clear what legal basis their vow was based on, but Akanat said the Thai constitution has an article that may enable the appointment of a new executive body by the Senate.

The appointment of a new premier by the anti-government group "is the red line not to be crossed," said Thailand-based author and academic David Streckfuss.

"The Red Shirts will rise en masse," he said referring to Shinawatra supporters who are due to hold a mass rally on Saturday in a Bangkok suburb.

Anti-government protest leaders, for their part, have vowed a "final fight" on Friday, without giving details of their plans.

Their pledge comes a day after the Constitutional Court removed Yingluck from office for abusing her power in the 2011 transfer of a security official

The ruling Puea Thai party swiftly appointed a deputy premier and commerce minister -- Niwattumrong Boonsongpaisan -- as Yingluck's replacement.

The party accused the court of a "conspiracy" against their administration, many of whose ministers are loyal to Thaksin Shinawatra -- Yingluck's billionaire brother and a former prime minister ousted in a military coup.

They want new elections slated for July 20 to drag the country from its political quagmire.

'Judicial coup'

Thaksin is adored by the rural, poor northern portion of the country for his populist policies, but reviled by the Bangkok-based establishment and southern royalists who accuse him or corruption and undermining the revered king.

Shinawatra-led or linked governments have won every election since 2001.

Anti-government protesters want an appointed "People's Council" to implement loosely-defined reforms aimed at eradicating Thaksin's influence on Thai politics.

At least 25 people have been killed and hundreds more wounded in political violence since they flooded Bangkok's streets and there are fears of wider clashes between pro- and anti-government supporters as the crisis snowballs.

Thailand's National Anti-Corruption Commission (NACC) may rule on Thursday against Yingluck on negligence charges linked to a costly rice subsidy scheme, which could lead to a five-year ban from politics.

Puea Thai fears the new cabinet could also be skewered by the NACC ruling, therein completing a "judicial coup".

"We hope any decision will be confined to Yingluck," Noppodon Pattama, Thaksin's legal adviser told AFP.

"There are no charges against the new cabinet, so to rule against them would be both highly illegal and against 'natural justice' ... but we have to wait and see."

Red Shirt chairman Jatuporn Prompan accused the court and NACC of "teamwork" with the anti-government protesters in an attempt to pincer the ruling party -- which under Yingluck won a landslide election in 2011.

Warning of an imminent military coup, in a country that has seen 18 successful or attempted coups since 1932, he urged Red Shirts to join a major rally on Saturday.

The kingdom has been bitterly split since 2006 when an army coup deposed Thaksin.

He now lives overseas to avoid jail for corruption convictions, that he says were politically motivated.

On Wednesday Yingluck became the third premier of a Thaksin-aligned government to be forced from office by the courts.