But hours later, police were instructed to get the protesters out of airports "as soon as possible" in a "peaceful manner", Nattawut Saikuar, a government spokesman, said.
"Firstly, the police should open negotiation with the protester.
"If they refuse to go, police should do whatever is necessary to open the airports on the basis of non-violence," he added.
The protesters led by the People's Alliance for Democracy (PAD), however, remained defiant on Friday, vowing to "fight to the death" if police tried to disperse them.
|Key facts: The PAD
Group is a loose coalition of royalists, businessmen and urban middle class -Thailand's traditional elite.
PAD led protests that triggered 2006 coup against the then PM, Thaksin Shinawatra.
Supporters wear yellow shirts, a colour associated with Thailand's revered king.
Group accuses Thaksin supporters of pushing to turn Thailand into a republic, an allegation rejected by Thaksin.
Critics say PAD's contempt for results of three democratic elections show it is neither popular nor democratic.
Click here for more on the PAD
"We are ready to defend ourselves against any government's operations to get us out of those places," Parnthep Wongpuapan, a protest leader, told The Associated Press.
"We are going to stay at the airports until Somchai resigns."
Al Jazeera's Step Vaessen, reporting from Suvarnabhumi, said things were calm at the airport on Friday and government officials appeared to be in negotiations with the protesters.
The government has said the airport will remain shut until at least Saturday and a military air base was being used, meanwhile, to help get some of the stranded tourists out of the country.
Thailand's political standoff began three months ago when the PAD occupied the prime minister's office compound and has paralysed the government, battered the stock market and dealt a serious blow to the country's $15bn tourism industry.
The PAD says protesters are waging their "final battle" to force the government out of office.
The European Union had earlier voiced concern over the situation in Thailand, warning that an "anti-constitutional attempt to interfere in the democratic process would have a negative impact" on ties, in a clear reference to speculation of a possible military intervention.
Nattawut, the government spokesman, said the prime minister had urged the army to stay in its barracks amid rumours of an imminent coup.
He also denied rumours that Somchai planned to sack Anupong Paochina, the army chief, a day after the general called for the premier to step down and call a snap election to defuse the country's political crisis.
The military has consistently said it will not carry out another coup after its 2006 move to oust Thaksin Shinawatra proved unsuccessful in solving the country's political woes.