Metropolitan Police commissioner Lt-General Wiroj Chantarangsi said the bombing might have been caused by the same group of people who threw rotten eggs at the protesters last month.

Protester Ittipol Sorawitkul, 60, said he saw a suspicious looking man riding a motorcycle around the tents in which the activists were sleeping outside the Srijulasup Building at around 4.25am. Later, he heard a bang and saw that a tent was on fire, he said.

Pieces of an energy-drink bottle were found at the scene, he said.

"We have been harassed since we began our sit-in protest. People have thrown things into our tents, including rocks. A mentally ill man tried to set fire to our tents and yesterday, a man with tattoos all over his body tried to get our group riled up and start a fight. The protesters were frightened but we won't give up," he said.

Wiroj said police would increase patrols in the area.

Anti-government activists have been protesting against the April 2 election in front of the building since late March. The group is demanding the election commissioners resign.

Late last month, a group of teenagers reportedly threw bags containing rocks, rotten eggs and messages attacking the protest at the group.

Kanpinat Sathirakul,

Suparat Iamtarn

The Nation