A police bomb expert holds up a defused home-made bomb found planted outside the Democrat Party’s headquarters yesterday. At right is Democrat Party deputy leader Alongkorn Pollabutr.

A bomb timed to explode at the same time a Democrat Party executive meeting was slated to kick off yesterday was politically motivated, party spokesman Ong-art Klampaiboon said.

He said he thought it was probably related to the party's campaign against alleged campaign violations relating to the funding of small parties.

Other party heavyweights echoed his views.

"I am sure the bomb was politically motivated," Democrat secretary-general Suthep Thaugsuban said.

Suthep said the bomb would not deter him from uncovering evidence of electoral fraud, claiming he and his fellow Democrats were duelling with government "thugs".

Ong-art said he was certain the bomb was meant as a threat.

Street sweeper Nidnoy Maensiri noticed a suspicious-looking box left next to the party's Kuang Apaiwong Building, housing offices for key party executives and reporters on the party beat, at about 6.30am yesterday.

Nidnoy quickly alerted the party's cleaning crew and security guards. Party officials and guards then reported the matter to Bang Sue police.

Four patrolmen said they thought it might have been a bomb and the anti-bomb squad was called in to destroy it.

"The bomb, if triggered, would have caused damage within a 50-metre radius," bomb squad chief Senior Sergeant Akkradej Pakkara-soong said.

The explosive consisted of two TNT sticks with a combined weight of 340 grams attached to a timing device.

The bomb was set to explode at 10.50am, coinciding with the start of the party's executive meeting.

Metropolitan Police Commissioner Lt-General Wiroj Chantharangsri assigned his deputy Maj-General Krisda Phankongchuen to investigate the attempted bombing.

Police have beefed up security at Democrat Party headquarters and other political installations in light of this incident and the prevailing political turmoil.

"Police are taking precautions because a third party might try to exploit and inflame the situation," Metropolitan Police spokesman Colonel Pinit Maneerat said.

Caretaker Prime Minister Thaksin Shinawatra said some ill-intentioned people might want to stir up trouble, adding he had no idea who planted the bomb.

Deputy PM Chidchai Vanasatidya said police had yet to draw a conclusion on the matter, but he ruled out speculation the attempted bombing might have been an attempt to derail the upcoming polls.

Thai Rak Thai spokesman Sita Divari also denounced the bomb. He expressed sympathy to the rival party but said the incident was "an easy trick" aimed at tarnishing TRT's reputation.

In another development, about 50 police officers were yesterday dispatched to guard Thai Rak Thai headquarters on New Phetchaburi Road after a group of Ramkhamhaeng University students tried to blockade it on Saturday.