Colombian President Juan Manuel Santos vowed to capture those responsible for detonating a homemade bomb that killed three people, including a French woman, in a busy shopping mall over the weekend and threatened to undermine years of security gains.

Santos offered a reward of around $35,000 to anyone with information about Saturday's attack at the upscale Centro Andino in the heart of the city's tourist district. The bomb, placed behind a toilet in a second-floor women's bathroom, went off as the mall was filled with Father's Day shoppers.

Much attention has focused on the National Liberation Army, the last major rebel movement still active in Colombia, which has carried a spate of recent attacks against mostly police targets in the capital. But leaders of the group have repudiated the bombing and Santos refused to feed speculation on the possible perpetrators to not interfere in the investigation in its critical, early phase.

In appealing for calm and unity, Santos touched on Colombia's long history of successfully combating drug-fueled violence and political extremism, saying the latest attack wouldn't derail peace efforts that have already resulted in a peace deal with the country's main guerrilla movement, the Revolutionary Armed Forces of Colombia.

"The Colombian people have the temperance, the resilience and the bravery to fight terrorism successfully," he said Sunday after a meeting with his top security aides. "You can be sure we're not going to let what we've achieved so far be stopped by a handful of extremist coward or people who don't want to see reconciliation in Colombia."

Later, he had a Father's Day lunch at the mall with his son, encouraging others to go about their normal activities. Dozens of Colombians gathered to decry violence, some of them leaving flowers in honor of the victims.

Of the nine mostly women who suffered injuries, only one remained hospitalized, Santos said.

The 25-year-old French woman who died, Julie Huynh, had been in Bogota since February volunteering at a school in a poor neighborhood as part of a master's program in international humanitarian aid. She was preparing to return to France in the coming days with her mother, who was with her in Bogota.

In a cruel irony highlighting how fragile Colombia's peace remains, the French-backed charity where she worked helps families displaced by the country's long conflict.

"From the very beginning Julie showed incredible commitment and energy toward the construction of a culture of peace in Colombia as evidenced by her work with youth on after-school activities," the group, Proyectar Sin Fronteras, said in a statement. The group posted on its Facebook page a black ribbon in memory of Huynh as dozens of emotional messages poured in from people moved by her example.

French President Emmanuel Macron, who will meet Santos this week as part of a previously scheduled visit to Paris by the winner of last year's Nobel Peace Prize, expressed his condolence to the victim's family while his government condemned the attack "with the greatest firmness."

"France stands at the side of Colombia in this painful moment," the Foreign Ministry said in a statement.

The ELN, which is engaged in long-running peace talks with the government, rejected accusations it was behind the attack.

"We ask for seriousness from people making unfounded and reckless accusations," ELN negotiators at peace talks taking place in neighboring Ecuador said on Twitter. "This is the way people are trying to tear up the peace process."

The ELN in February claimed responsibility for a bombing near Bogota's bullring that killed one police officer and injured 20 other people. But the group, which is much smaller than the FARC, said it doesn't target civilians.

Penalosa urged residents of Bogota's wealthier districts to be on high alert but cautioned that there was no hint that other attacks being planned.

Some analysts attribute an uptick in violence in Colombian cities to the ELN's desire to wrest concessions from the government at the negotiating table. They also have expressed doubts about the ELN leadership's ability to control its roughly 1,500 troops, given that the group has traditionally operated with a much looser command structure than the highly-centralized FARC, which also condemned the attack.

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 have let down their guard.

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

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Goodman reported from Caracas, Venezuela. AP Writer Angela Charlton contributed to this report from Paris.