By Viparat Jantraprap
BANGKOK, May 17 (Reuters) - Anti-government protesters in Thailand are to stage mass rallies in coming days to try to get a new prime minister installed, but their leader said if this final push in a six-month fight did not succeed, he would surrender to the authorities on May 27.
"It's time. This show has been going on for so long," Suthep Thaugsuban told a meeting of supporters from around the country on Saturday. "It must come to an end. Whether it will be a happy ending depends on the great mass of people in this country and our state officials."
Thailand has been in turmoil since the protests flared up in November, the latest phase in nearly a decade of antagonism between the Bangkok-based establishment and supporters of former premier Thaksin Shinawatra, who won huge support among the rural and urban poor but was ousted by the army in 2006.
Thaksin's sister, Yingluck Shinawatra, was forced to step down as prime minister on May 7 when the country's Constitutional Court found her and nine ministers guilty of abuse of power.
Remaining cabinet members selected Commerce Minister Niwatthamrong Boonsongphaisan to replace her, but the anti-government protesters led by Suthep said they had no authority to do that and want all the ministers replaced.
Suthep told Saturday's meeting - held in Government House, where the prime minister normally works but which he has commandeered - that the mass rallies would start on Monday.
Ahead of that, he would meet with state company officials and sympathetic retired civil servants on Sunday to draw up plans for a new administration and then he wanted to meet serving top civil servants on Thursday.
Thailand has not had a lower house of parliament since December, when Yingluck dissolved the house and called a general election. Voting was disrupted by Suthep's supporters and the election was then declared void by the Constitutional Court. A proposed rerun on July 20 is looking increasingly unlikely.
The upper house Senate, half of whose members are appointed and many of them establishment figures with views close to Suthep, is trying to break the impasse.
On Friday, after a meeting of a limited group of senators, its newly elected speaker said the Senate was prepared to choose an interim prime minister but members wanted to speak to political parties first. They will meet the government on Monday.
Suthep wanted more immediate action and is now putting pressure on the Senate to hurry things along.
He has set numerous deadlines for the government to step down in recent months and issued many ultimatums, including telling civil servants and the security forces to report to him, to little effect.
However, his powers of disruption remain.
Acting premier Niwatthamrong was forced to flee from a meeting with election officials on Thursday when Suthep led his supporters into the air force compound where the talks were being held.
Niwatthamrong runs a caretaker government with limited authority and Senate head Surachai argues that a prime minister with full powers is needed to get the country out of the political and economic mess.
Data on Monday is expected to show the economy contracted in the first quarter as confidence slumped and investment dried up because of the political crisis. Some economists fear the economy is slipping into recession.
Pro-Thaksin "red shirts" camped in their thousands on the outskirts of Bangkok say they will defend the government if it looks like being forced out.
Thaksin, who now lives in exile to avoid serving a jail sentence for abuse of power, is a former telecoms tycoon who is adored by the poor for policies that raised their living standards from 2001. Opponents say he was corrupt, authoritarian and disrespectful towards the monarchy.
Twenty-eight people have been killed in political violence since November, including three during a gun and grenade attack on anti-government protesters in Bangkok on Thursday.
The attack prompted the army chief to warn that his men "may need to come out in full force" if violence escalated.
(Writing by Alan Raybould; Editing by Matt Driskill)