A bomb exploded Friday at a Spanish-owned bank on the outskirts of Mexico City, the latest in a series of attacks against foreign financial institutions in the last four years.
The explosion shattered glass, wrecked computers and tossed furniture on its side, but caused no deaths or injuries.
The device went off just below the window at a branch of Bancomer, owned by Spain's Banco Bilbao Vizcaya Argentaria, Mexico State Attorney General Alfonso Navarrete said at a news conference. Mexico State is home to many sprawling suburbs of the Mexican capital.
Navarrete described the explosive as a "rudimentary" device.
In the wreckage, police found a letter claiming responsibility for the attack from the previously unknown Barbarous Mexico Revolutionary Workers' Commando, Navarrete said.
The same group sent an e-mail to The Associated Press railing against "neoliberal reorganization and capitalist expansion."
The e-mail specifically criticized U.S. businesses in Mexico, including Wal-Mart and McDonald's and the U.S.-backed proposal for a Free Trade Area of the Americas. U.S. President George W. Bush and Mexican President Vicente Fox have been pushing for the free-trade zone, which would stretch from Canada to Chile.
The group also claimed responsibility for a second bomb in front of another Bancomer in a nearby neighborhood. Luis Rivera, director of Mexico State's emergency services, said a second explosive device was found on fire but failed to detonate.
Friday's explosion was similar to other bombings at foreign-owned banks in recent years.
In May 2004, devices exploded outside three banks in Jiutepec, just outside Mexico City. The overnight explosions caused major damage but no injuries. Those bombs targeted branches of Banamex, BBVA-Bancomer and Santander Serfin. Explosives left outside a HSBC bank did not go off.
Authorities found a note near the 2004 bombing sites signed by a group calling itself the Comando Jaramillista Morelense 23 de Mayo - in tribute to the peasant leader Ruben Jaramillo, who was murdered along with his family by government forces on May 23, 1962. The note criticized Fox's pro-business policies.
In August 2001, three explosives packed into tin cans detonated and two more were defused at branches of Banamex, which was being purchased by U.S.-based Citibank. A small leftist group called the Revolutionary Armed Forces of the People claimed responsibility.
Police arrested five alleged members of the group and charged them with organized crime and terrorism. The men were acquitted because of lack of evidence.