BOGOTA, Colombia -- Colombia's leading presidential candidate was unharmed Sunday after a bomb exploded near his motorcade in an apparent assassination attempt, killing three bystanders and injuring 15 others.

Alvaro Uribe, a hard-liner running on pledges to crack down on leftist guerrillas, was traveling through the Caribbean coastal city of Barranquilla when a bomb placed under a bridge exploded just after his caravan and a passenger bus crossed over.

Five police officers and 10 civilians were injured, including two children and the bus driver and passengers, officials in Barranquilla said.

Uribe appeared on local television and radio moments later to confirm that he was unharmed in the blast, which occurred shortly after the motorcade pulled away from a campaign event at the city's port.

"It must of been a very powerful explosive because I was traveling in the most heavily armored kind of vehicle, and the vehicle was destroyed. But thank God, here we are, talking," Uribe, 49, told Caracol Radio. He said nobody traveling with him was hurt.

Remote control device

General Armando Sandoval, the police chief in Atlantico, said the wounded police officers -- two in serious condition -- were assigned to protect Uribe. The blast was triggered by remote control, Sandoval added.

"Attributing blame at this moment would be speculation," Sandoval told local RCN radio. "We know that it was a remote control device."

Ricardo Galan, an Uribe spokesman, said the injured police were motorcycle escorts assigned to the motorcade.

A 3-year-old girl walking along the road lost one of her legs, Galan added.

Galan said there was "no doubt at all" that it had been an assassination attempt. He predicted Uribe would have to cut back his public appearances drastically and make more use of the media to get out his message.