Suspected insurgents detonated a motorcycle bomb that killed three security volunteers Sunday in Thailand's insurgency-plagued south, following explosions the previous night that left one person wounded, police said.

An explosive device hidden in a motorcycle went off in the commercial district in the city of Pattani on Sunday morning, killing three civilian security volunteers who were on duty at a tower clock and wounding nine other people, Police Col. Tuanday Juthanan said.

Pattani is one of three Muslim-dominated southernmost provinces in predominantly Buddhist Thailand. More than 5,000 people have been killed in the region since an Islamist insurgency erupted in 2004.

On Saturday night, suspected militants planted seven bombs across Pattani city, but security forces managed to defuse five of them, Tuanday said, adding that one person was wounded in the two blasts.

Prime Minister Yingluck Shinawatra declined to comment Sunday on whether the attacks were in response to the killing by marines of 16 militants this past week at a marine corps base in Narathiwat, another mostly Muslim province. It was the deadliest toll the Muslim guerrillas suffered since more than 100 died in a single day nearly a decade ago.