BANGKOK, March 18, 2010 (AFP) - Thailand's prime minister on Thursday said he was open to negotiations with red-shirted protesters who have massed in the capital to demand that he step down and call snap elections.

"If the demonstration is still within the law the government does not object to holding negotiations (with protesters)," premier Abhisit Vejjajiva said in a nationally televised conference.

"The government is open for participation," he added, without giving further details of the format the talks could take, two days after making a similar offer.

Since the rallies began, Abhisit has stood firm against the demands by protesters, mainly backers of ousted fugitive premier Thaksin Shinawatra, whose numbers swelled to 100,000 at the peak of their rally on Sunday.

"I am sincere about holding reasonable talks but the rally must be within the law. If not, it's unacceptable to me," Abhisit said.

The rallies appear to have been peaceful so far, but have used shock tactics such as splattering the premier's house and office with blood.