Police on Aug. 27 issued arrest warrants for nine protest leaders on a variety of charges including insurrection, which carries a maximum penalty of death or life imprisonment. On Friday, another key figure, Chaiwat Sinsuwongse, was arrested on the same charges.
The nine, who are members of the People's Alliance for Democracy, led mass street demonstrations which led to the ouster of Prime Minister Samak Sundaravej last month.
Police spokesman Maj. Gen Suraphol Thuanthong police earlier told The Associated Press that authorities were preparing to arrest all the remaining nine at the appropriate time and place.
Thousands of members of the alliance have occupied Government House since Aug. 26. They have said they will not leave until allies of deposed Prime Minister Thaksin Shinawatra are no longer in power.
The arrest warrants against the nine include charges of insurrection, conspiracy, illegal assembly and refusing orders to disperse. Insurrection is the legal equivalent of treason.
The protest alliance has accused the government of Prime Minister Somchai Wongsawat of acting as proxy for Thaksin, his brother-in-law, who was ousted in a 2006 military coup.
Somchai replaced Samak, who was forced from office last month when a court ruled that he violated a constitutional conflict of interest provision by accepting money for hosting a TV cooking show while in office.
Because of the siege of the prime minister's office compound, Somchai has been forced to set up a temporary office at Bangkok's old airport. The new premier has tried to open negotiations with the protest leaders, but so far no formal talks have taken place.
Thaksin, a billionaire telecommunications tycoon, was toppled by the Sept. 19, 2006, military coup after months of demonstrations led by the same protest alliance, which demanded he step down because of alleged corruption and abuse of power.
However, Thaksin's allies swept back into power in December elections. Thaksin has since fled to London to escape a string of corruption charges.