Antigovernment activists plan to defy a tough security law to rally Saturday on the third anniversary of a military coup.
Webmasters face criminal charges for comments posted on their websites deemed offensive to the royal family.
Attack on Sondhi Limthongkul could further weaken the economy and strengthen hard-liners
The prime minister Friday extended the state of emergency he declared last week after rival protesters descended on the capital.
In Bangkok Tuesday thousands ended their sit-in and leaders surrendered, saying they wanted to avoid violence but continue their campaign.
Security forces were mobilized for the first time since 2006 as violence escalates – two people died in street clashes Monday.