A strong explosion from a bomb rocked one of the busiest shopping centers in Colombia's capital, killing three people, including a 23-year-old French woman, and injuring nine others, authorities said.

Witnesses told of being evacuated from movie theaters and stores after the blast yesterday in a second-floor women's restroom at the upscale Centro Andino in the heart of Bogota's tourist district. Ambulances and firetrucks rushed to the scene and the injured were taken to a hospital, where two later died.

Police said a bomb from an undetermined explosive had caused the destruction. Mayor Enrique Penalosa called it a "cowardly terrorist bombing." 

He said the French victim, identified as Julie Huynh, had been in Colombia the past six months volunteering in a poor neighborhood and was preparing to return to France in the coming days. He said authorities were providing assistance to the victim's mother, who was also in Bogota.

Authorities' attention immediately focused on the country's largest still active rebel group, the National Liberation Army, or ELN, which in February claimed responsibility for a bombing near Bogota's bullring that killed one police officer and injured 20 other people.

Penalosa urged residents of Bogota's wealthier districts to be on high alert but cautioned that there was no hint of other attacks being planned. Police said they were still trying to determine what the device that exploded was made of.

The government last year reached a peace deal with the Revolutionary Armed Forces of Colombia, which was much bigger than the ELN. The ELN is also engaged in peace talks but has so far refused for its fighters to lay down their weapons.

Some analysts attribute an uptick in violence in Colombian cities to the group's desire to wrest concessions from the government at the negotiating table.

Bogota has seen dramatic improvement in security over the past decade as the country's long-running conflict has wound down. But the capital remains vulnerable to attacks as residents let down their guard.

Still, the Andino shopping center would seem a difficult target. All vehicles entering the parking garage are screened by bomb-sniffing dogs and security guards are present throughout the mall.

President Juan Manuel Santos said he was returning immediately to Bogota and ordered the head of Colombia's police to lead the investigation and keep him regularly updated. In a message posted on Twitter he expressed his solidarity with the victims.