The Pak Chong district schools closed after panicked parents withdrew their children following rumours of bomb threats.

"I received a call from a man in the late morning who claimed to be a parent and told me he had seen a television news report about bomb threats at the school," Pak Chong School director Direk Saeson said.

"When I asked him the name of his child, he hung up," Direk said. He heard later other schools in the district had received similar calls.

The rumour reached parents, who took their children home.

"We contacted the military, and two sniffer dogs were sent to search the school compound. We found no bomb," Direk said.

Pak Chong police said a cleaner at the Khao Yai National Park had heard from a park official that the Pak Chong market and night bazaar were targets for bomb attacks. The official was said to have heard the rumour from a Bangkok Metropolitan Administration officer. The story was passed along until it reached parents of students.

"The rumours have no solid ground. However, as a precaution, we have dispatched nine teams of sniffer dogs across the district to check areas considered risky," Pak Chong police inspector Major Patiyuth Singsomroj said.

In Kanchanaburi, a bomb-disposal team destroyed a bag found near the provincial city hall. Copper wire and black tape were visible in the unattended bag. It was later determined the bag was harmless.

In Bangkok a man telephoned the Office of the Narcotics Control Board and said a bomb had been planted there and was timed to explode at 11.40 am. Staff were evacuated. No device was found.

Police inspected an unattended bag at a bus stop near the Chinese Embassy. It turned out to be harmless.