Supporters of Sri Lanka's sacked prime minister and a top election official on Monday challenged in court the president's dissolving of parliament, upping the ante in a political crisis that has sparked international alarm.
Late on Friday, President Maithripala Sirisena called snap elections and dissolved the legislature, two weeks after sacking the prime minister and installing the divisive Mahinda Rajapaksa in his place.
The United States has led a chorus of international concern over events in the Indian Ocean island nation of 21 million people.
Three political parties holding an absolute majority in parliament and an election commissioner, one of three officials tasked with conducting polls, on Monday asked the Supreme Court to declare the president's actions illegal.
Commissioner Ratnajeevan Hoole was among 12 petitioners arguing that Mr Sirisena had violated the constitution.
In the five-page petition, Mr Hoole said the president broke the law in calling the snap elections for January 5 after a string of unconstitutional moves since October 26 when he forced out Ranil Wickremesinghe, the prime minister.
Mr Wickremesinghe's United National Party, the main opposition Tamil National Alliance and the leftist JVP, or People's Liberation Front, jointly filed the action.
TNA spokesman M A Sumanthiran said the Supreme Court agreed to take up the petitions immediately considering the importance of the issue.
"We are also asking for an interim order" for an injunction against preparations for the election, which would be two years before schedule, Mr Sumanthiran said.
Court officials said Chief Justice Nalin Perera and two other judges decided to fast-track the hearings.
Sarath Amunugama, Mr Sirisena's anointed foreign minister, told Colombo-based diplomats on Monday that he expected a verdict within five days.
Legal experts say the dissolved parliament would have to be restored if the Supreme Court rules in favour of the petitioners. If not, the January 5 election will have to go ahead.
Independent election monitors have also questioned the legality of the snap poll.
Mr Wickremesinghe remains in the prime minister's official residence, and both he and Mr Rajapaksa are attempting to run parallel administrations.
On Sunday night, parliament speaker Karu Jayasuriya urged civil servants to defy Mr Sirisena's "illegal orders".
But Mr Sirisena defended his actions, saying violence among rival MPs could have led to "civil unrest" across Sri Lanka if the legislature had met as scheduled this week.
"Had I allowed the parliament to meet on November 14, there would have been violence in the House and it could have spread to our villagers and towns," he said in a televised address.
"I acted to prevent civil unrest."
Mr Sirisena's rivals maintain that he had no constitutional power to sack the assembly until it completed four-and-a-half years of its five-year term that ends in August 2020.
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Only China has recognised the appointment of Mr Rajapaksa, who during his decade as president until 2015 relied heavily on Beijing for diplomatic and financial support as the West shunned him.
While in power Mr Rajapakse ended Sri Lanka's four-decade civil war by crushing the separatist Tamil Tigers. But 40,000 ethnic Tamils were allegedly massacred in the process.
Seventeen journalists and media workers were killed during his time in power, and Mr Rajapaksa and his family have been accused of using his period in office to line their pockets through corruption.
A meeting of diplomats called by Mr Amunugama on Monday was boycotted by several western diplomats while others sent low-level representatives, diplomatic sources said.