Mexico City ? Mexico’s government said Tuesday that a series of gas pipeline explosions were attacks aimed at weakening the nation’s democratic institutions after a small, leftist rebel group claimed responsibility.

The Interior Department said it was stepping up security at “strategic installations” across Mexico after an explosion Tuesday at a pipeline run by the state-owned Petroleos Mexicanos, or Pemex, and two other blasts that rocked gas ducts Thursday. No one was injured in the blasts.

While officials said investigations were continuing into the cause of the blasts, the statement by the Interior Department – responsible for domestic security – came a short time after a small guerrilla group said its members had planted explosives on the pipelines.

It was impossible to independently confirm the claim, made by the “military zone command of the People’s Revolutionary Army,” or EPR.