BANGKOK, June 19 (Xinhua) -- A leading international NGO on human rights on Friday condemned the teacher-killings by suspected insurgents in deep south of Thailand, and called on the authorities to take appropriate measures to bolster security at schools, Thai media reported.

    "In a sickening trend, separatist insurgents are increasingly attacking teachers, who they consider a symbol of government authority and Buddhist Thai culture...There is no excuse for such brutality," The Nation online quoted Brad Adams, Asia director of the New York-based Human Rights Watch, as saying.

    Thailand's deep South, which includes mainly the three southernmost provinces Yala, Pattani and Narathiwat as well as some parts of Songkla province, has undergone violence by suspected separatists for years, during which more than 3,500 people have been killed since 2004.

    Among the recent killings, two female teachers, one of them eight-month pregnant, were shot to death by alleged insurgents on June 3 in Narathiwat province, bringing to 113 the number of teachers killed in the unrest over the past five years.

    And the latest case is on Tuesday, when a female teacher of Poh-meng School in Raman district of Yala province was shot dead on her way to school.

    According to The Nation, the spike in violence came immediately after a controversial verdict by Thai court on May 29, which cleared Thai security forces of any wrong doing in their handling of the Tak Bai massacre, an incident that ended in the death of 85unarmed Malay Muslim demonstrators, 78 of whom died from suffocation when they were stacked on the back of military truck one on top another.