People who lost power when the Thaksin Shinawa-tra regime was overthrown were behind the string of bombs in Bangkok on Sunday - not insurgents from the South, Prime Minister Surayud Chula-nont and junta chief Sonthi Boonyaratglin said yesterday.

Four former aides and top officials to Thaksin, including the former PM's Secretary Dr Prommin Lertsuridej and former deputy PM Chidchai Vanasatidya, have been summoned for questioning.

But none has reported to the authorities so far.

The Council for National Security planned to train owners of petrol stations, super-markets and factories, plus their workers, as security guards to help prevent what Sonthi called the "new threat" in urban areas.

"The military has been trained to handle this type of threat and urban sabotage for two years since we have known it could happen in our country," he said.

"We've got some links to the masterminds but never expected they would do something like this. They wanted to hurt the economy, spoil political and social stability," Sonthi said.

Eight bombs went off in several areas of Bangkok on New Year's Eve, killing three people and injuring 37, including nine foreigners.

"The bombers were ill-intentioned people who want to create a political impact. I would like all Thais to be aware of their intentions and that they want to create a scenario of politically instability in Thailand," Surayud said during a press conference at the office of Internal Security Operations Command (Isoc).

Prime Minister Surayud called an Isoc meeting with all concerned security agencies to discuss the situation while Sonthi - just back from the Hajj in Saudi Arabia - called a CNS meeting yesterday.

Officials have beefed up security at public places in the capital, including the new airport and bus terminals, as a lot of people are due to return from trips to see their families today and tomorrow.

Surayud said his claim was based on evidence - residue in the explosives, plus the location and timing of the blasts.

However, he refused to say clearly whether "the people who lost political benefits" referred to followers of the ousted Prime Minister Thaksin Shinawatra or not.

The pattern of explosions and situation suggested the bombs in Bangkok were not linked to on-going violence in the deep South, Sonthi said.

"The militants are in trouble, even in Yala. I don't think they would come here as they could get lost in Bangkok," Sonthi told reporters.

Thaksin, who is now in exile and currently in China, strongly denied insinuations he was involved in the deadly bomb blasts. He suggested it may have been the work of Muslim separatists from the deep South, his lawyer said.

"Thaksin strongly rejects the allegations and said that his government, which came from the people, would not hurt its people," Noppadon Pattama said.

"The government should not rush to conclusions by trying to relate the attacks to previous governments. It is totally unfair and untrue," he said.

Noppadon said Thaksin warned coup leader General Sonthi some time ago to keep a close watch on militants from the far South in case they carried out bomb attacks in Bangkok.