Mexican President Vicente Fox called a special meeting of his security advisers on Thursday following three overnight bomb explosions in Mexico City attributed to a shadowy insurgent group. Authorities are not certain who set the bombs or why.

In his meeting with cabinet members and security advisors, President Fox called for a complete investigation of the group claiming responsibility for the bombings - the People's Revolutionary Armed Forces, or FARP. Anonymous callers claiming to represent the insurgent group called Mexican news media offices to say they had placed the homemade explosive devices at several locations around the city. But authorities say it is difficult to determine if the bombings really were carried out by the FARP or by some other group.

Attorney General Rafael Macedo de la Concha says his office will be investigating the issue thoroughly. He said investigators will be analyzing the information they obtain about the bombings, and that it is already known that the FARP has cells in the city as well as in some nearby states.

The Mexican Attorney General says he hopes the Mexico City Prosecutor's office will hand the case over to federal authorities so that they may do a more complete investigation of the case.

The three explosions all occurred at branch banks belonging to the Banamex chain, which was recently purchased by the Citigroup banking corporation. The small bombs did no more than break windows at the banks. Two other devices were found by police and safely disarmed. The bombings occurred several hours after farm workers had staged a mass demonstration in Mexico City to protest the Fox government's agricultural policies.

The FARP is one of several small guerrilla groups that have emerged in Mexico in recent years. Masked men claiming to be part of the insurgency staged a brief takeover of a town square near Mexico City on December first of last year - the day Mr. Fox was inaugurated president. Authorities say the bombings may have been a way to gain attention in that they appear not to have been intended to harm anyone.