Three grenade blasts - two of them targeting banks - left seven people injured in this northeastern Mexican city, officials said.

The Tamaulipas state Attorney General's Office said the three explosions occurred before midday Friday in different parts of the state capital, while another explosive device was deactivated.

It said the first grenade was detonated inside an HSBC bank branch at a shopping center, injuring six people and damaging the customer service area.

The second attack outside a branch of the Banamex bank, a Citigroup subsidiary, injured one person and caused damage to the building and four parked cars.

No one was hurt in the third grenade blast, which occurred on a street between two official vehicles that were parked outside a home.

The fourth grenade, discovered in the parking lot of a federal building, was deactivated by army and federal police explosives experts.

In an operation immediately after the attacks, state and federal police detained a suspect identified as Juan Bernardo Zapata, 21, who has prior convictions for vehicle theft and for serving as a lookout for drug-trafficking gangs, the state AG's office said.

He was riding a motorcycle at the time of his arrest.

Mexico's Attorney General's Office is joining state authorities in the investigation because the use of explosives is a federal crime.

Last month, seven police were injured in Tamaulipas in a grenade blast a roadside hotel in the city of Nuevo Laredo.

In March, a car bomb exploded outside the offices of the Expreso newspaper in Ciudad Victoria; no one was harmed in the explosion, which caused damage to buildings and vehicles.

Tamaulipas, which borders the U.S. state of Texas, is a key smuggling corridor being fought over by Mexico's most powerful drug cartels, including the Zetas gang and an alliance of the Sinaloa and Gulf mobs. EFE