
The explosion occurred at 3:25 am just 50 metres from the right side of the stage where leaders of People's Alliance for Democracy addressed the demonstrators.
The bomb fell onto a tent and exploded, causing a one-metre-wide hole on the tent's roof.
The explosion initially caused a panic among the protesters, but the protest leaders managed to control the situation minutes later and calmness returned to the rally site.
Following the explosion, PAD guards sealed of the area to preserve evidence.
At 4:15 am, Gen Pathompong Kesornsuk, a senior military officer who sympathised with the protesters, announced to the crowd that the bomb might be launched with an M29 launcher into the compound.
He said all the evidences had been collected to be given to Army chief Gen Anupong Paochinda to investigate.
Pathompong said the Army chief would be urged to provide protection to the people inside the Government House.
He said the PAD would also step up security.
He said an investigation should also be carried out to determine whether Gen Kattiya Sawasidphol, an army expert, was involved with the latest explosion because Kattiaya had threatened the protesters with bomb attacks.