Thousands of teachers have joined strikes

Luc Ferry's comments came as teachers in the southern city of Perpignan stopped students sitting their key baccalaureate exams for a second day.

Teachers across France have been striking and marching through the streets in protest at reforms including decentralisation and pension changes.

In Perpignan, nearly 2,000 students missed their exams on Monday when teachers blockaded the building, and more tests were postponed there on Tuesday.

They have the right to strike, to protest, to be in disagreement, but they do not have the right to take children and their families hostage and I will not accept it Luc Ferry Education Minister

Some exams were also postponed in schools in Toulouse.

Protests elsewhere included a take-over of toll booths on a motorway near St Etienne, and roads being picketed in Le Havre.

Education ministry offices in Lyon were also blockaded.

Mr Ferry told French radio he absolutely backed their right to strike, but not to impede the children's futures.

"They have the right to strike, to protest, to be in disagreement, but they do not have the right to take children and their families hostage and I will not accept it," he told French radio station RTL.

He was drawing up "very firm" measures, he said, to avoid a general postponement of exams, which he described as "totally unacceptable".

We try to talk to the teachers but they don't listen. We are not against them. We agree with their cause. But we do not want these constant strikes French pupil

He had various legal means at his disposal, he added, to deal with the situation, although he did not elaborate.

The French Government insists that its reforms are needed - on pensions to head off a crisis over too many retired people, and on education structure to create a better financial structure.

Mr Ferry insisted that, although many details were open to discussion, he would not be deterred by street protests and would not resign.

"If I were replaced it would make absolutely no difference," he said.

A line has been crossed that should not have been Christian Janet Parents' association

"Reforms are essential and there is no question of withdrawing them to buy social peace. This will not be the case of yet another minister giving in and then resigning.

Mr Ferry will meet union leaders later on Tuesday to discuss the situation. Main teaching unions have said they do not support exam blockades.

Some parents groups have reacted angrily to the threat to exams.

"A line has been crossed that should not have been," said Christian Janet, head of the PEEP parents' association.

And in the town of Angers in central France, more than two dozens pupils staged their own rival protest.

"We try to talk to the teachers but they don't listen. We are not against them. We agree with their cause. But we do not want these constant strikes," said one pupil.

A big day of anti-reform strikes on Monday saw hundreds of thousands of public sector workers taking to the streets. An even bigger day of strikes took place last Tuesday.