Three simultaneous explosions occurred late Sunday night in Mexico City, destroying an entrance at the headquarters of a leading political party and apparently affecting the Federal Electoral Tribunal and a bank branch.

The government news agency Notimex said there were no immediate reports of injuries.

Mexico City Fire Department official Daniel Flores told The Associated Press that authorities were responding to the scene, but he had no additional information.

At the headquarters of the former ruling Institutional Revolutionary Party, or PRI, the entrance to an auditorium located on one side of the building had been destroyed, its door blown out, according to an Associated Press photographer at the scene.

Chunks of concrete, shattered glass and the concrete bust of former Mexican President Plutarco Elias Calles, the PRI's founder for whom the auditorium is named, lay scattered on the ground. There appeared to be little damage immediately inside the building.

Police investigators used flashlights to sift through the rubble, but declined to talk to the news media.

A PRI representative told radio station Formato 21 the explosions were probably carried out by groups trying to destabilize the government before President-elect Felipe Calderon's swearing-in on Dec. 1. Calderon is a member of the ruling National Action Party of President Vicente Fox.

No one answered the telephone early Monday at the offices of the civil protection branch responsible for the area.