Seven police officers were hurt Thursday when a bomb detonated at a hotel in the Mexican border city of Nuevo Laredo, authorities said.

The blast occurred at 7:30 a.m., a source in the Tamaulipas state Attorney General's Office told Efe.

The injured state police officers were taken to a hospital in the city, which lies just across the border from Laredo, Texas.

Authorities are still trying to determine whether the bomb was inside the motel or in a car parked outside.

The explosion at the motel followed arson attacks on three Nuevo Laredo nightclubs and coincided with gunbattles on city streets, media outlets said.

Nuevo Laredo has been rocked in recent weeks by major clashes between gunslingers from the rival Sinaloa and Los Zetas drug cartels, which are vying to control smuggling routes into neighboring Texas.

The Mexican army took charge of public safety in the city nearly a year ago amid concerns that the municipal police department had been penetrated by organized crime.

Conflict among cartels and between criminals and the security forces has claimed more than 50,000 lives in Mexico in the last 5 1/2 years. EFE