Supporters of the ousted Prime Minister Yingluck Shinawatra warned yesterday that installing an unelected leader, a demand of anti-government protesters that has helped to drive months of unrest in which dozens have been killed, could lead to "civil war".
Tens of thousands lined the streets of Bangkok for the protest by the pro-government supporters – their first since Ms Yingluck was ousted last week, along with nine other ministers.
Jatuporn Prompan, a leader of the pro-government protests, warned that putting in place an unelected prime minister would "create a serious crisis that could lead to a civil war that no one wants to see".
The rally comes after anti-government protesters ramped up their efforts to bring down what remains of Ms Yingluck's administration on Friday.
They laid siege to television stations, surrounded state offices and demanded officials help them to install a non-elected prime minister to rule the country – having been given fresh impetus by the Constitutional Court ruling that dismissed Ms Yingluck.
Police fired tear gas and water cannons to push back hundreds of anti-government demonstrators who attempted to force their way into the government's security agency, leaving at least a dozen injured.
"Although it is hot out here, our anger is hotter. We are boiling with anger. I am ready to give this fight everything I've got," said Sombat Thammasuk, 44, a "red shirt" supporter of Ms Yingluck.
A government security official said about 50,000 people had joined the rally and more were expected. Gathering under a sweltering sun, many said they were prepared to stay for days to press for an election, which a caretaker government is working towards holding on 20 July. Ms Yingluck's cabinet has named deputy premier Niwattumrong Boonsongpaisan as acting prime minister.
Anti-government supporters were also out on the streets again yesterday. Tension mounted as police prepared to keep the two sides separated for fear of confrontations which have, in the past, become violent, with at least 25 dead and hundreds injured since demonstrations over the government began last November.
Thailand's politicians have been unable to forge a compromise over a nearly decade-long split between the royalist establishment and the influence of a populist former telecommunications tycoon, Thaksin Shinawatra, sister of Ms Yingluck, who was ousted in a military coup in 2006.
The leader of the anti-government protest movement, Suthep Thaugsuban, said yesterday that Mr Niwattumrong "doesn't hold the authority and status to be the head of the government."
"The caretaker government is unlawful, which means at this stage Thailand has no real government," Mr Suthep told reporters at a rally.
Mr Suthep called his supporters out on to Bangkok's streets for what he says will be a final push to get the government out. He said the Senate should "quickly consult the presidents of the Supreme Court, the Constitutional Court, the Supreme Administrative Court and the Election Commission to work to appoint the new prime minister immediately."
He then wants to install a "people's council" to oversee reforms aimed at excluding Mr Thaksin from politics. Mr Thaksin lives in self-imposed exile to avoid a jail term handed down in 2008 for corruption, but has been a major influence over his sister's government. The group has already disrupted elections that were held back in February.
The unrest in the country has led to foreign investment in South-east Asia's second-biggest economy plummeting, and tourism has waned as the situation has rumbled on.