* PM Abhisit says Asian summit will go ahead this week
* Number of protesters smaller than organisers expected
* Thaksin asks protesters to stay "three more days"
By Kittipong Soonprasert
BANGKOK, April 8 (Reuters) - Thai Prime Minister Abhisit Vejjajiva insisted on Wednesday that an Asian summit, postponed once already, would go ahead in Thailand this week despite a mass rally in Bangkok by demonstrators intent on toppling him.
Police said 100,000 demonstrators, supporters of ousted former premier Thaksin Shinawatra, were at Government House and the nearby Royal Plaza by the evening, more than during the day but still far fewer than the 300,000 organisers had promised.
No clashes were reported, although fears of violence fed rumours that a meeting of leaders of the Association of South East Asian Nations (ASEAN) and other Asian countries starting on Friday would be cancelled or shifted to another venue.
Abhisit dismissed such talk in a phone interview with Channel 9 television on Wednesday evening.
"I'd like to stress that we are going ahead in holding the ASEAN summit as scheduled," he said.
The meeting was postponed late last year because of political unrest when a pro-Thaksin government was in power, and Abhisit's administration has billed the rescheduled event as a sign Thailand was getting back to normal. [ID:nSP435860]
Thaksin was toppled in a coup in 2006 and is in self-imposed exile, but his absence has not healed the divisions between the royalist and business elite, who accused him of corruption, and the poor who benefited from his populist policies.
Thaksin called into the rally over a live video link in the evening and told his supporters to stay put until the weekend.
"This is not about me, this is about bringing real democracy to Thailand, this is about the country. I ask everyone who believes in democracy to join the rally and stay for three more days," he said.
The country celebrates a big holiday, Songkran, from April 13-15 and demonstrators are likely to disperse by then.
Thaksin moves around, popping up recently in Dubai and Hong Kong. He was convicted on conflict of interest charges last year.
Government spokesman Panitan Wattanayagorn said several members of Thaksin's immediate family had left the country in the past few days, possibly out of fear for their safety.
On Tuesday Abhisit's car was attacked by Thaksin supporters after a cabinet meeting in the resort town of Pattaya, where the ASEAN summit will be held. He was unhurt. [ID:nBKK418437]
"As to the minor incident at Pattaya yesterday, the security standard for my normal working days and that for leaders attending the coming summit will be entirely different," he told Channel 9, adding all the government leaders would be turning up.
Officials said troops could be brought in to beef up security if that was thought necessary.
The pro-Thaksin United Front for Democracy against Dictatorship (UDD) has besieged Abhisit's office at Government House since March 26. The protest has been peaceful, but security was tightened on Wednesday because of the mass rally.
The UDD says the army engineered Abhisit's election as prime minister by parliament in December with the help of defectors from the previous pro-Thaksin government.
Abhisit has kept away from his office for the past two weeks, part of it spent in London representing ASEAN at the G20 summit.
The prospect of renewed violence has added to the concerns of the stock market .SETI, which has fallen 1.4 percent this year while many Asian markets have recovered, but the index rose after the central bank cut interest rates on Wednesday. [ID:nBKT000962]
One target of the demonstrators' anger is Prem Tinsulanonda, 88-year-old chief adviser to King Bhumibol Adulyadej. Thaksin has accused Prem of playing an active role in the 2006 coup, an allegation the former army general and prime minister denies. A group of more than 1,000 demonstrators marched from Government House to Prem's nearby home, which was guarded by riot police. There was no violence and UDD leaders called for calm.
"I came here to drive Prem out and stay until he quits," said red-clad protester Paiboon, a food vendor. "He led the coup that caused our country a lot of damage and drove a good person like Thaksin out of the country." (Additional reporting by Martin Petty, Arada Therdthammakun, Vithoon Amorn and Panarat Thepgumpanat; Writing by Alan Raybould; Editing by Paul Tait)