Riot police and protesters have clashed at a university campus in the Mexican city of Oaxaca in the latest protests against the state governor.
Protesters inside the university threw petrol bombs at riot police
At least eight people were injured in the clash. Police used water cannon and teargas as crowds threw petrol bombs.
Last week, 4,000 riot police entered Oaxaca, removing demonstrators from the city centre after five months there.
Striking teachers and leftist activists are demanding that Governor Ulises Ruiz be sacked for alleged abuse of power.
The Mexican senate recently urged Mr Ruiz to resign, but he has so far refused.
Reports say federal police were initially pushed back from the state university by hundreds of protesters guarding the entrance.
The protesters threw petrol bombs at riot police who had been pushing forward through barricades of burnt out vehicles, eyewitnesses told Reuters news agency.
But the police were supported by helicopters and armoured vehicles.
Many activists retreated to the university after they were forced out of the city centre at the weekend.
Police were not allowed to enter the premises. Under Mexican law police must seek a permission by a university rector.
The protests in Oaxaca were initially run by teachers striking for better pay and conditions, but they expanded to involve other groups who accuse Mr Ruiz of electoral fraud.
The protests began in May, virtually paralysing the city.
The teachers initially staged the walk-out to demand higher pay and better working conditions.
However, after police attacked one of their demonstrations in June, they extended their demands to include a call for the governor's resignation.
The teachers were then joined in their protest by left-wing groups.
Thousands of schools have been closed since the strike began, leaving 1.3 million children unable to attend classes.