Arson attacks on five schools and a bomb blast caused jitters in southern Thailand on Tuesday, but the prime minister appealed for calm.
No-one was injured in the attacks, radio and television reports said.
The 12 October bombing of a tourist resort on the Indonesian island of Bali, which has been blamed on Muslim extremists, has left South-East Asia on alert.
Prime Minister Thaksin Shinawatra has said Thailand is not at risk from international terrorism and he quickly ruled out foreign involvement in Tuesday's attacks.
"It is a local problem and it will not be difficult to find out who did it," he told reporters.
Mr Thaksin also said he believed those responsible for the arson attacks were not involved in a series of murders of police officers in the area earlier this year.
Pre-dawn attacks
One bomb exploded on the stairs of a Buddhist temple before dawn on Tuesday while another was found and defused at a Chinese temple in Yala.
In neighbouring province of Songkhla, there were a series of fires at five schools, also before dawn. One building was destroyed and several others were damaged.
Songkhla province is mostly Buddhist, like the rest of Thailand, but it has a large Muslim minority. The past year's violence has largely been in the neighbouring Muslim-dominated provinces of Yala, Pattani and Narathiwat.
The area has experienced Muslim separatist violence in past years, but most analysts now believe any militant groups are small and are not capable of carrying out major attacks.
Police Chief Sant Sarutanond said that the fires, which appeared to be carried out by a single group, were aimed at damaging Thailand.
"They didn't want money or to take lives, they wanted to discredit the country's image," he told reporters.
"They wanted to create a situation because this region (South-East Asia) has a problem but Thailand doesn't. It has been done by a group of people who have ill will against Thailand."
Malaysia and Singapore have warned Thailand that Islamic militants may try to hide in Thailand. Western countries have warned of possible attacks in tourist resorts such as Phuket.