HAT YAI, Thailand — A well-respected Muslim cleric in Thailand's violence-plagued south was killed on Monday in one of the highest-profile assassinations of those working with the Thai government in resolving the southern insurgency.

Imam Yacob Raimani, 50, was shot dead by an unidentified gunman who came with three other suspected insurgents at a market in Pattani city, Police Col. Tuanday Juthanan said on Monday. He said the militants fled on two motorcycles.

Yacob was known to sympathize with Thai authorities in their bid to end the violence and was against radicalization. He survived an assassination attack in 2011.

Human Rights Watch researcher Sunai Phasuk said Yacob's death could silence other Muslim sympathizers in the region.

"This is a message of terror to what they call 'Muslim collaborators' in the region, in order to make them cease their connection with the Thai authorities," Sunai said. "It will also make the local community leaders that sympathize with the peace process withdraw themselves from being vocal about their support."

The shooting took place during the Ramadan period. Muslim separatist negotiators have said they would attempt to halt all violence in insurgency-plagued provinces throughout the Islamic fasting month.

Six security officers and five civilians were killed in three other attacks in the three Muslim-dominated southernmost provinces on the same day.

More than 5,000 people have been killed since an Islamic insurgency erupted in the sub-region in 2004.