A 51-year-old Bulgarian was in critical condition on Thursday after he set himself on fire, the fourth self-immolation in protests against poverty and corruption that have brought down the government.
All the other protesters who set themselves on fire over recent weeks have died, in the most graphic expression of the public anger that is now aimed against a day-old caretaker administration.
"The cup of people's anger overflowed. There is nothing to wait for and we will start new protests," the leader of one protest movement, Yanaki Ganchev, said at a protesters' encampment near parliament before a rally planned for 6 p.m. (1600 GMT).
The latest self-immolation happened outside the president's offices on Wednesday as career diplomat Marin Raikov took over as interim Prime Minister, appointed by the head of state to guide Bulgaria into elections in May.
"It (the interim government) is just another attempt at replacement and not real change," said Ganchev, leader of the Eagles' Bridge protest movement, named after a crossing in Sofia that is a rallying point for demonstrators.
Protesters distrust the interim government because Raikov and three others members served in previous conservative cabinets. Other interim ministers also have links to the right-wing GERB party which led the last administration, they say.
Bulgarians have protested for more than a month, at first against high electricity prices in the European Union's poorest country.
Grievances spread to more general concerns about living standards of less than half the EU average, and a political elite accused of maintaining a corrupt system since the collapse of communism in 1989.
President Rosen Plevneliev named Raikov to lead a team of technocrats, hoping their records as experts would mark a clean break and ease public anger.
Raikov moved swiftly to reassure financial markets by pledging to keep spending under control, after Bulgaria brought its budget gap down to 0.5 percent of national output, but also said he would work with protest leaders to find ways of helping society's poorest, including pensioners.
People in the country of 7.3 million live on an average monthly wage of 400 euros ($520) and pension of less than half that.
The size of protests has dwindled in the last week and protesters show few signs of forming a movement that could run for election, suggesting the established parties will govern again.
That may ease investor concerns that demands for increased spending might upset fiscal stability or a currency peg to the euro, but it also means public discontent could simmer and boil over into new protests in future.
Angel Slavchev, who heads another protest faction, the National Citizen's Initiative, also doubted the new government's independence but said it should be given a week to prove its worth.
"People are fed up with the fact that nobody wants to hear them and there may be some violent protests if the government does not take urgent steps," Slavchev said.