A protest against Mexico's 20-percent gasoline price hike turned violent Saturday after a lone protester drove his truck into a line of police guarding a fuel distribution terminal in Baja California.
Federal police said four officers were injured in the incident in Rosarito, near the border city of Tijuana.
Video showed the small pickup driving straight into the line of riot police, then backing up and speeding off.
Largely peaceful protests against the fuel price increases continued elsewhere in Mexico Saturday, and looting seen earlier in the week largely subsided. But nervousness remained.
Officials in Veracruz, one of the states hardest-hit by the looting on Wednesday and Thursday, said some neighborhood groups had begun to form patrols of residents armed with staves or machetes to ward off looters.
Veracruz Gov. Miguel Angel Yunes Linares said 532 people had been detained in his state alone and that social rumors of further looting — apparently unfounded — had caused "an artificial psychosis."
He said that in the northern part of the state, given this psychosis, "the neighbors decided to arm themselves with staves, machetes, creating the impression that there were armed groups of criminals."
Yunes Linares said the government was trying to convince residents to stop such patrolling.
The Interior Department reported a total of more than 1,500 people have been detained for looting or disturbances nationwide since protests began early in the week.
It is unclear how many have been charged. Hundreds of stores were looted, mainly on Wednesday and Thursday. Police protection of stores has been stepped up since.
The federal police reported continued protests, and some highway blockages, on Saturday.
Thousands of people marched down main avenues in the western city of Guadalajara Saturday to protest the increases, which are part of a government effort to deregulate fuel prices.
Despite persistent rumors that political interests might have egged on the looters to smear the gas-hike protesters, Yunes Linares said there was "no evidence that political parties were involved." He said authorities were investigating whether criminal gangs had taken part.