A grenade launched from an M-79 yesterday landed in a parking area within the NBT compound off Vibhavadhi Rangsit motorway in Bangkok, causing no casualties but damaging property.
State-run NBT - formerly known as Channel 11 - was the target of attacks during the red-shirt protests in March and April.
Bangkok police chief Lt-General Santhan Chayanont and PM's Office Minister Ong-art Klampaiboon, who oversees the Public Relations Department-run NBT, both said the attack was politically motivated.
The lone grenade was fired into a parking lot in front of the main NBT office around 1.30pm, damaging four vehicles.
Santhan said the grenade could have been launched from the ground rather than a vantage point on an elevated tollway in front of NBT, as policemen were manning the section as security for a royal motorcade.
Ong-art later commented that the grenade should not have targeted NBT personnel as new NBT policies give more chance for opposition figures and NGOs to speak freely on state-run channels.
A meeting of police and civilian investigators was held later. Three teams of investigators have been assigned to compile evidence and conduct a trajectory study to determine where the grenade was fired from.
Chief investigator Pol General Phanupong Singhara na Ayutthaya said a potential lead was that those behind the two blasts near the King Power complex in Soi Rangnam could have been behind the latest attack on NBT.
Meanwhile, reporters covering the police beat were assessing a rumour that Santhan could be transferred from Metropolitan Police chief in a reshuffle to be announced next month, because the police have failed to stem blasts in Bangkok and have made no arrest or breakthrough after five bomb attacks in the capital.
Phanupong did not rule out the possibility of the grenade being fired from a moving vehicle on the tollway, and ordered that all security camera footage on the tollway be inspected.
Prime Minister Abhisit Vejjajiva said it was difficult for security agencies to deal with political activities in a mixed variety of illegal and peaceful events. "It would have been easier to maintain security if these two types of activities were separated clearly from each other," he said, without explaining.
"If we are too strict with security measures, public liberty will be affected, but if we completely set everything free, I believe violence will be widely used," he said. Abhisit also called on those wishing to express themselves legally to carry out activities separately from those associated with illegal means.
Commenting on frequent statements by opposition Pheu Thai MPs predicting attacks, he said it was their right to speak. "But I would rather they give authorities tip-offs on where and how the attacks will be carried out."
Mathee Supapong, director of the Bank of Thailand's Domestic Economy Department, said the recent bombing incidents would dent investors' confidence a little.
"Let's hope that the government is able to nail down the culprits soon," he said.
But he said he personally did not worry about the incidents much as he believed the situation would not spiral out of control.