At least three people were killed and another 18 wounded in a bomb explosion at a market in Thailand on Monday, an official said.The bomb was planted on a motorcycle parked in Pimolchai market in Yala, capital of the province of the same name, a police official told Efe news.Initial investigations suggested that the device was placed next to a pork stall.Attacks using small arms and bombs are frequent in the southern provinces of Pattani, Yala and Narathiwat despite the deployment of 40,000 security personnel and a state of Emergency.More than 6,700 people have died in clashes in the region since the Muslim separatist movement resumed its armed struggle in 2004, according to the monitoring organisation Deep South Watch.