Thailand's opposition Tuesday launched a legal attempt to annul a controversial weekend general election, as the US warned against any attempt at a military coup to end months of political agony.

Thai Prime Minister Yingluck Shinawatra answers questions from the press after voting at a polling station in Bangkok on February 2, 2014  

 A lawyer for the opposition Democrat Party filed a petition in the Constitutional Court to invalidate Sunday's protest-hit polls and disband the ruling party -- the latest in a series of challenges through the notoriously interventionist courts to Prime Minister Yingluck Shinawatra's government.

"The petition is to seek to nullify the election, disband Puea Thai party and ban its party executives from office for five years," Virat Kalayasiri told reporters as he entered the court, later confirming it had been officially lodged.

Yingluck called Sunday's snap election to try to defuse mass rallies that have dogged her government for three months, sparked deadly violence in Bangkok and thrust the kingdom into prolonged political turmoil.

But the protests, led by a former Democrat MP, have continued -- raising the spectre of a "judicial coup" to end the impasse, which has also seen demonstrators besiege official buildings and occupy key intersections in the capital.

The protesters want Yingluck ousted and her government replaced by an unelected "People's Council" to enact vaguely-defined reforms before new elections.

They say she is a mere puppet for her exiled elder brother, former prime minister Thaksin Shinawatra whom they accuse of corruption and vote-buying.

The Democrats, Thailand's oldest party, boycotted the poll while opposition-backed protesters prevented 10,000 polling stations from opening on Sunday, affecting several million people, mainly in opposition strongholds in Bangkok and the south.

Virat said the legal challenge pivots on the government's failure to hold full elections, after the protest disruption prompted election authorities to withhold results until ballots are cast in all constituencies.

"The government failed to hold the election on the same day. It was an attempt to gain power unconstitutionally," he said, adding that he had filed the petition on a personal basis.

Bitter Divides

Yingluck's government now faces a series of legal challenges, including one over alleged corruption linked to a controversial rice subsidy scheme and an effort to change Thailand's senate to make it fully elected.

"It's a political game to discredit Puea Thai and Yingluck's government," said party spokesman Pormpong Nopparit.

Observers say the powerful army, which has staged numerous coups in the past, is reluctant to step in this time despite calls from anti-government protesters for it to resolve the crisis.

But in the most outspoken comments so far by an ally, the United States warned against any moves to stage a military coup.

"We certainly do not want to see a coup or violence," US State Department spokeswoman Jen Psaki said after opposition protesters prevented voting at thousands of polling stations on Sunday.

"We remain concerned that political tensions in Thailand are posing challenges to the democratic institutions and processes of Thailand."

The country's bitter polarisation hinges on the influence of Thaksin, who was ousted as prime minister by a coup in 2006 and lives in self-imposed exile.

He is adored by the rural poor in the north and northeast but loathed by the Bangkok middle class and southerners.

The billionaire-turned-politician or his allies have won every election since emerging onto Thailand's political stage more than a decade ago.

But he was deposed soon after his second electoral win in 2006 and two elected Thaksin-backed parties were subsequently dissolved by the courts.

Puea Thai has hailed Sunday's election as a victory for democracy after ballots were cast by nearly half of those voters whose local polling stations did not close.