Sri Lanka's Prime Minister Ranil Wickremesinghe suffered his first setback after taking office on Thursday when a leading opposition MP rejected his invitation to take the post of finance minister in a unity government.
Mr Wickremesinghe, 73, was appointed after his predecessor Mahinda Rajapksa resigned amid violent nationwide protests over an economic crisis that has caused months of shortages, rising prices and blackouts.
The veteran politician, who has been prime minister five times before, said he was confident of getting enough support to steer the country through the crisis and approached several potential allies to join his administration.
But on Friday opposition MP Harsha de Silva, an economist, publicly rejected an overture to take charge of the nation's finances and said he would instead push for the government's resignation.
“People are not asking for political games and deals, they want a new system that will safeguard their future,” he said in a statement.
He said he was joining “the people's struggle” to topple President Gotabaya Rajapaksa, the former prime minister’s younger brother, and would not support any political settlement that left the leader in place.
Mr De Silva is a member of the Samagi Jana Balawegaya (SJB) party, the largest opposition grouping in parliament, which had appeared ready to split over the question of whether to support Mr Wickremesinghe.
But the head of the possible splinter faction, Harin Fernando, said on Friday he had returned to the fold.
"I will not support Wickremesinghe's government," Mr Fernando told AFP.
Two smaller parties also signalled that they would not join a unity government.
The Tamil National Alliance said Mr Rajapaksa's administration had "completely lost legitimacy" with the appointment of Mr Wickremesinghe, who most recently held office in 2019.
The leftist People's Liberation Front (JVP) meanwhile said new national elections were the only way out of the current impasse.
Mr Wickremesinghe is the only member of parliament from his United National Party and must rely on rival political parties to form a government. An alliance led by the president and his brother holds about 100 of parliament's 225 seats, while the opposition has 58 seats. The rest are independent.
Hundreds of people remain camped at a protest site in the capital Colombo, demanding that Mr Rajapaksa step down.