A few minutes later, bombs exploded outside of the headquarters of the Institutional Revolutionary Party (PRI), a Scotiabank branch and the Federal Electoral Tribunal building. Two more improvised explosive devices (IEDs) were defused later outside of another Scotiabank branch and another PRI building. No serious injuries have been reported.

Although those responsible for the bombings have not been identified, Mexico is facing political and social unrest from two separate camps -- suggesting one of the two, or perhaps a sympathetic outside group, is upping the ante.

Most of the bombs contained approximately 11 pounds of the commercial blasting compound hydrogel, making them fairly large devices (the IED defused outside the PRI building contained just about 1 pound of explosives). Moreover, Mexican security officials said the IEDs were more sophisticated than the kinds of devices seen in previous attacks in the capital, although these were the first bombings in Mexico City since November 2005. At that time, an anti-globalization group calling itself the Barbarous Mexico Revolutionary Workers' Commando detonated two similarly sized bombs outside of two banks, one U.S.-owned and one Spanish-owned.

The tactics employed in the Nov. 6 bombings are similar to those used in the past by leftist groups such as the Popular Revolutionary Army (EPR) and its various splinters. Although the bombs were larger than those normally used, they were operated on battery-powered timers that were set to detonate at night, when fewer people would be in the area. The defused bombs even had warning signs affixed to them that read "Danger -- Bomb."

The bombings could very well be related to the unrest in Oaxaca state, where an annual teacher's protest has spiraled into a full-blown insurrection that has seen leftists and other opposition groups demand the removal of state Gov. Ulises Ruiz of the PRI.

The People's Popular Assembly of Oaxaca (APPO), the main group in the poorly organized and loosely affiliated movement in Oaxaca, denied later Nov. 6 that it had any part in the bombings. The involvement of militants from the region or groups sympathetic to the APPO cause, however, cannot be ruled out. Even if the APPO leadership did not order the bombings, some of the group's fringe members -- those who believe the group's leadership is unwilling to take the necessary measures -- might have decided to take matters into their own hands.

Just last month, the crisis in Oaxaca took a more violent turn when previously unknown leftist group Revolutionary Armed Organization of the People of Oaxaca (ORAPO), detonated three small IEDs at banks in the troubled state. The ORAPO, however, claimed responsibility for that attack in a letter left at one of the sites. So far, no group has claimed responsibility for the Mexico City attacks.

The bombings also could be related to this summer's controversial presidential election. Supporters of failed candidate Andres Manuel Lopez Obrador have been increasingly vocal about the strife in Oaxaca -- and could be planning to co-opt it into their agenda. The Federal Electoral Tribunal, which issued the ruling on the contested election that denied Lopez Obrador a victory, could have been targeted by his supporters.

If the bombings are directly connected to Oaxaca, it indicates the unrest that spread from rural Mexico to the capital is escalating. If the bombings are related to the elections, it suggests the opposition is raising the ante while the government tries to deal with the situation in Oaxaca. With both issues unsettled, the remnants of the EPR, its splinters  or groups acting on behalf of the Oaxacans would have no shortage of motivations to carry out similar attacks.

Regardless of the motive, these bombings have serious implications for future stability and security in Mexico. President-elect Felipe Calderon, who had hoped to avoid having to deal with the Lopez Obrador or Oaxaca situations when he takes office Dec. 1, will likely find that both issues continue to fester -- and probably escalate. As long as the situation in Oaxaca is unresolved, the risk of similar attacks in the capital will remain.