Police are investigating whether recent violence in Chiang Mai, Bangkok and Chon Buri is related to the political conflict.
Police have stepped up security for certain independent agencies and courts, as well as at the homes of certain important figures and judges following recent violent attacks, according to Royal Thai Police deputy spokesman Pol Maj-General Anucha Romayanant.
Grenades were fired and thrown at locations linked to agencies and officials dealing with cases against government politicians.
A police meeting yesterday, chaired by deputy national police chief Pol General Aek Angsananont, agreed to the need to heighten patrols around those locations in order to prevent more attacks by "people with ill intentions who want to create some incident", the spokesman said.
The focus would be on the risky areas within a 400-metre radius around those places, he said, adding that police checkpoints have been set up in some areas.
Police also would ensure that security cameras and bomb-disposal personnel would be ready for action in case they are needed.
A distance of 400 metres is within the effective range of grenades fired from an M79 launcher, which has become the weapon of choice for the perpetrators in attacks over recent years.
Three separate violent incidents involving grenades occurred in the northern city of Chiang Mai on Friday night, leaving four people injured - one of them seriously, according to police.
In the eastern seaboard province of Chon Buri, two grenades were fired into a building that houses the Bang Sai administrative organisation's office at about 9.30pm on Friday. Part of the building and two cars parked inside were damaged. There were no reports of injuries.
Police said the intended target of the attack could be the nearby rally site of the anti-government protesters linked to the People's Democratic Reform Committee (PDRC). The rally had attracted about 2,000 people when the attack occurred.
PDRC local leader Kantapon Sukhumalin said it was lucky that the grenades fell short of the rally site, otherwise there could have been many injuries.