The teachers, from Narathiwat province, have vowed not to reopen schools until security is improved.

Violence flared up earlier this year, with Islamic militants targeting officials, teachers and police.

More than 200 people have been killed since January, and dozens of schools have been torched.

The teachers' protest was triggered by the shooting last week of a teacher and student by a pair of gunmen on a motorbike.

More than 80% of the 400 schools in Narathiwat province will now be closed, at least until Friday.

According to the Bangkok Post newspaper, the teachers accused the government of failing to find a solution to the violence, which they said was spiralling out of control.

Prime Minister Thaksin Shinawatra angered the teachers further, by saying they should be happy with the bonus they receive for working in the troubled south.

"We have already paid a risk premium to teachers which means they have to take those risks. If they do not want to, please move elsewhere," he told reporters on Wednesday.

''If they can't stand the heat, get out of the kitchen,'' he told the Bangkok Post.

Thawat Sae-ngam, president of the teachers' union in Narathiwat province, said the 1,000 baht ($25) monthly allowance was not worth risking teachers' lives.

"If Thaksin wants the money back, he can have it, but the schools will continue to be closed until the government comes up with a satisfactory solution," he told the Associated Press news agency.

Union leaders have called for co-operation from nearby provinces to back the strike action, but teachers in the other two southern provinces of Yala and Pattani decided not to join the strike due to lobbying by provincial governors.