Thailand's army on Thursday told anti-government protesters to disperse from their rally base, warning that a crackdown will be launched and their "time is running out".
"In order to disperse the mob, the authorities will be very decisive and there will be chaos," said army spokesman Colonel Sunsern Kaewkumnerd. "This is not a threat, this is real."
"We don't want you to risk your lives. If there is a clash you could be hurt by stray bullets," he added. "Your time is running out. Please leave the area and report to the authorities.
The army spokesman said that in the crackdown, the authorities "will target the protest leaders as a first priority".
Sunsern said that the demonstrators who leave the rally encampment -- which covers a large swathe of Bangkok's retail and hotel district -- would not face any charges.
"If you leave and report to authorities then you will not be prosecuted but after we take action then you will be arrested and prosecuted," he said.
Sunsern said there were currently 6,000 of the red-shirted protesters at the site, down from 14,000 on Wednesday evening when bottles and stones were thrown in confrontations between the Reds and pro-government demonstrators.
The Reds have refused to withdraw and ruled out talks with the government, saying there was no room for compromise after street clashes in Bangkok earlier this month that left 25 people dead.
Entrances to the vast Red Shirts encampment have been fortified with barricades made from bamboo poles and car tyres draped with plastic sheeting.
Piles of sharpened bamboo sticks and broken paving stones have been stockpiled, triggering fears of new confrontations with security forces who are threatening to use tear gas and live fire if necessary.