The governor of Yala says the bombs went off Saturday around lunchtime in Yala city's business area.
Authorities say the bombs, hidden in two motorcycles and a car, also set several nearby buildings on fire.
A separate blast in nearby Songkhla province claimed at least three lives and injured more than 200 people. Officials are blaming the explosion at a high-rise hotel in the city of Hat Yai on a gas leak.
Bombings, like those Saturday in Yala, are a common tactic of Islamic separatists who have been waging an insurgency in the Muslim-dominated provinces of Yala, Narathiwat and Pattani since early 2004. The conflict has taken more than 5,000 lives.
