Mexican riot police used tear gas and water cannon on Thursday (November 2) to force back Molotov-cocktail hurling protesters as violence flared again in the strife-torn city of Oaxaca. Federal police who took over the city centre at the weekend in an attempt to end a political conflict that has killed more than a dozen people, were earlier pushed back by hundreds of protesters guarding the entrance to the state university, a protest nerve centre. The protesters, who have blockaded Oaxaca for five months demanding that state Gov. Ulises Ruiz step down, threw petrol bombs at riot police who had been pushing forward through barricades of burnt-out vehicles. But the grey-clad riot police regained the upper hand as reinforcements arrived in armoured trucks and helicopters, spraying protesters with water cannon and firing tear gas canisters. Protesters said one demonstrator was injured in the clash. Mexico's government earlier said in a statement that police would not enter the university. Strict rules prevent government security forces from entering autonomous state universities. Outgoing President Vicente Fox sent federal police to the colonial city after gunmen apparently linked to local officials shot dead three people on Friday (October 27), including a U.S. activist and journalist. Oaxaca's state government said in a statement that it had arrested two people thought to be involved in the killing. Local media said on Thursday the two belonged to Ruiz's opposition Institutional Revolutionary Party. Accusing Ruiz and his government of corruption and of using thugs to crush dissent, the protesters forced local and state police out of the city in June, took over offices, sentenced people accused of theft and charged street corner tolls.