Mexico ? Two bombs were planted Friday at branches of a Spanish-owned bank on the outskirts of Mexico City, the latest in a series of attacks against foreign financial institutions in recent years. One bomb failed to detonate and the other caused no injuries.

The first device exploded before dawn just below the window of a branch of Bancomer, owned by Spain’s Banco Bilbao Vizcaya Argentaria, said Mexico State Atty. Gen. Alfonso Navarrete. The bomb shattered glass, wrecked computers and overturned furniture.

A second device, found at a nearby branch of the same bank, failed to detonate, police said.

In the wreckage of the first bomb, police found a letter claiming responsibility for the attacks 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” and singling out 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.