The bomb, which went off at about 1.30am, was planted in a garbage pile - a method similar to a bomb attack near Big C Rajdamri last Sunday. But this time it was a Chinese-made hand grenade that was used, while the Big C bomb attack relied on a US-made M67 grenade.

The unnamed victim, who is about 35-40 years old, was seriously wounded. Rajvithee Hospital, which is treating the victim in an intensive care unit, said the chance of his surviving was about 10 per cent.

A two-hour meeting of police and military officers was held yesterday morning to discuss investigation methods and security measures to prevent future bomb attacks. City administration and military officers are expected to be mobilised to keep a watchful eye on garbage-disposal sites and garbage piles.

After the meeting, Bangkok police chief Pol Lt-General Santhan Chayanont said collection times and other aspects of garbage collection might need to be changed to minimise the chance of attackers hiding bombs in garbage dumps and piles.

The detonation method of the King Power bomb was different from previous attacks. The safety lever was held with rubber bands soaked with petrol to release the lever slowly. He said this technique was intended by the attackers to confuse the public.

Asked whether he had a word for "an old man" he frequently referred to as a possible mastermind behind various bomb attacks, Santhan said: "I'd rather arrest him this time, I don't want to curse and scold him any more."

Police said there were nine security cameras near the blast site, but they had not found footage showing any suspicious act or anyone planting the grenade in the garbage pile.

Chief investigator Pol General Phanupong Singhara na Ayutthaya said police would in the meantime work on both bomb cases, and it had not been decided whether they would be taken over by the Department of Special Investigation.

Deputy Prime Minister Suthep Thaugsuban said the Defence Ministry had been assigned to boost intelligence work to curb bomb attacks.

Just hours before the attack, the Centre for Resolution of the Emergency Situation had designated Defence Minister Prawit Wongsuwan to take charge of intelligence gathering and security, he said. The CRES also instructed the Royal Thai Police, the lead agency in charge of security in the capital, to increase cooperation with the military for peacekeeping operations.

Prawit was scheduled to hold an intelligence meeting this morning aimed at detecting and foiling any bomb attacks.

Prime Minister Abhisit Vejjajiva later warned of possible further bomb attacks in Bangkok.

"It's likely that the bomb was aimed at inciting unrest," Abhisit said. "The overall assessment and evaluation of the situation is that more bomb attacks are likely at this time."