Homemade bombs exploded in two Buenos Aires banks before they opened Wednesday, killing a security guard, police said.
The explosions occurred near ATMs in branches belonging to Citibank and Banco Galicia, damaging the buildings' facades and shattering windows, officials said.
No group immediately asserted responsibility for the attacks.
The security guard, 38, was killed at a Citibank branch in downtown Buenos Aires, said German Fernandez, a spokesman for a private ambulance service.
Police said they also deactivated two explosive devices, and at least one officer was injured after authorities detonated a bomb found inside a second Citibank branch.
Banks remain a target of public anger following Argentina's 2001-2002 economic crisis.
Billions of dollars in bank accounts held by Argentines were frozen as the government tried to thwart a run on the banks and prop up a tottering financial system.
Since then, hundreds of thousands of Argentines have filed lawsuits hoping to recover their savings, much of which were forcibly converted from dollars to devalued Argentine pesos.
Lula Rodriguez, a Citigroup spokeswoman in Miami, said the company was cooperating with authorities investigating the bombings.
Police in Buenos Aires were put on alert and extra patrols were assigned to areas with a large number of banks, according to the police chief, Hector Giacardi.
The blasts were the latest in a string of bombings in recent months. A bomb exploded outside a Buenos Aires bank in August during a visit by the head of the International Monetary Fund, but did not cause any injuries. A second bomb was later found and deactivated outside of a McDonald's.