A coalition of five leftist guerrilla groups that support protesters in the southern state of Oaxaca claimed responsibility for homemade bombs that exploded at Mexico's top electoral court, a bank and the headquarters of the political party that governs Oaxaca.
The bombings across Mexico City early on Monday caused no injuries but rattled nerves in a country wracked by protests since the polarizing July 2 presidential elections.
President Vicente Fox called the attacks "criminal acts aimed at frightening the population."
Leftist protesters have battled federal police for control of Oaxaca City since last week, and the guerrilla groups pledged to continue "military" actions until Oaxaca state Governor Ulises Ruiz steps down.
Protesters accuse Ruiz, of the Institutional Revolutionary Party (PRI) of rigging the elections that brought him to power in 2004 and oppressing dissent, but have so far failed in their attempts to oust him.
"We take full responsibility for these actions," the groups said in a statement e-mailed to the news media. "Our political-military action is a response to our determination to reply with revolutionary violence to the violence unleashed by the lords of power and money."
The five groups are known to Mexican authorities and have claimed responsibility for bombings in the past, said Jose Luis Manjarrez, spokesman for Mexico's Attorney General's Office. But he said there is "nothing at this point to be able to confirm the veracity of the statement."
The groups identified themselves as the Lucio Cabanas Barrientos Revolutionary Movement, the Democratic Revolutionary Tendency-People's Army, the Insurgent Organization-May 1, the Dec. 2 Execution Brigade and the Popular Liberation Brigades.
The rebels said they would continue such actions as long as "repressive federal and local forces continue to repress the people," an apparent reference to the federal police raid of Oaxaca a week ago that pushed the protesters out of the city's main central plaza, which they had occupied since May.
About a dozen rebels claiming to represent the five groups appeared in a rural area of Oaxaca state in late August wearing masks, military-style uniforms and carrying assault rifles. At the time, they distributed leaflets supporting the cause of the Oaxaca protesters.