Four soldiers were wounded when three bombs exploded at a shelter inside a school's grounds in Thailand's restive southern province of Yala, Bangkok Post online reported Thursday.

According to police, six soldiers from Yala Task Force 14 who were on a security patrol went into the shelter inside the grounds of Samakkhi School in Yala's Yaha district to take a rest. Three bombs which had been planted there were detonated simultaneously at about 9.30 a.m. local time on Thursday.

The explosions wounded four soldiers and wrecked the shelter. The schoolchildren were all in their classrooms about 200 meters away at the time.

The improvised bombs, made of gas cylinders, weighed about 10 kg in total, police said. They blamed separatist militants for the blast.

Since the resurgence of insurgency in 2004, around 11,000 violent incidents instigated by secessionists in the Muslim- dominant southernmost provinces of Yala, Pattani and Narathiwat happened with almost 5,000 people killed and nearly 8,000 injured.