Gunmen have fired on striking teachers marching through the southern Mexican city of Oaxaca, killing one man.
Teachers want better pay and the governor's resignation
Protesters responded by setting fire to a house where the gunmen fled. They blamed Governor Ulises Ruiz for the attack, a charge his office rejected.
Tens of thousands of teachers have been on strike for weeks, demanding higher pay and the governor's resignation.
Mr Ruiz is accused of rigging the 2004 election to gain office and of using force to suppress dissent.
The killing of a teacher on Thursday came after months of mounting violence in the city.
The dead man was identified as 50-year-old Jose Jimenez.
A house where the bullets where believed to have come from was set on fire by the protesters.
A spokesman for the Oaxaca People's Assembly, which organised the march, said protesters had captured four suspected gunmen, the Associated Press news agency reports.
The city has seen continuing protests since June, after police attacked a teachers' rally.
About 2,000 people have been camping out in the centre of the city, where they have set up barricades and smashed windows.
A radio station and a newspaper which have expressed support for the protests have been attacked by gunmen - two reporters have been injured and equipment damaged and stolen.
On Wednesday, a group of Triqui Indians driving to the city to join the protests was ambushed and three people, including a 12-year-old boy, were killed. It is not clear whether their deaths were linked to the protests.