BANGKOK—A major international human rights organization called Monday for an immediate end to violence against school personnel in Thailand's insurgency-wracked southern provinces, following last week's murder of two Buddhist teachers who were shot execution-style in the middle of a school day.

New York-based Human Rights Watch said in a statement Monday that the Islamist insurgents who execute teachers show what it termed "utter depravity and disregard for humanity" and also threaten the security of the Muslim community that they claim to represent.

More than 5,000 people have been killed in the three Muslim-dominated southernmost provinces of Buddhist-dominated Thailand since an Islamist insurgency erupted in January 2004. The total includes 157 school personnel.

The insurgents' apparent goal is a separate state, and the conflict is partly fueled by a perception that ethnic Malays are discriminated against by the authorities in the Buddhist state.

On Dec. 11, five assailants wielding M-16 assault rifles infiltrated the Ban Ba Ngo school in the southern province of Pattani, according to Human Rights Watch' account . Upon entering a dining hall where seven teachers had gathered for lunch, they carefully selected their targets. Setting aside the five Muslim teachers, the insurgents set their sights on the two Buddhist educators in the crowd, Somsak Kwanma and Tiyarat Chuaykaew, the school's director. As Tiyarat sought shelter behind a Muslim teacher, she and her Buddhist colleague were killed on the spot.

Militants have killed three additional teachers and wounded three others over the past six weeks, said the group.

The latest killings took place while classes were in session, marking a darker turn for the turmoil in the region, where insurgents consider teachers at state-run schools legitimate targets because they are representatives of the Thai government.

Previous targeting of teachers had prompted state authorities to strengthen security measures and provide armed guards to escort the teachers to and from work, but not necessarily to supervise them during the course of the school day. Other schools limit travel by providing room and board for instructors.

In response to last week's killings, the Confederation of Teachers of Southern Border Provinces suspended classes for all 1,200 schools in the region on Thursday and Friday. Classes resumed Monday.

The most recent spate of attacks prompted Prime Minister Yingluck Shinawatra to make an official visit to the region last Thursday. On Sunday, she issued a statement on her official Facebook page, saying, "We have a vested interest in providing security and protecting the lives of our teachers," though no specific measures have been instituted yet.