Fifteen soldiers have been killed in an ambush in north-eastern Colombia, army officials say.
The explosion in Bogota occurred at the end of morning rush hour
They say the soldiers were on their way to investigate reports of an illegal checkpoint when they were attacked near the border with Venezuela.
No group said it carried out the ambush - which came hours after a bomb killed a civilian in the capital, Bogota.
The attacks came a week before President Alvaro Uribe is due to be sworn in for a second term.
The ambush against the army patrol occurred in Norte de Santander province - where left-wing rebels of the Revolutionary Armed Forces of Colombia (Farc) are known to operate.
Army commander Carlos Ospina said the soldiers responded to reports that rebels were concentrating there.
"It's deplorable, but the soldiers who were trying to establish security in the region walked into a mine field," Gen Ospina said.
In Bogota, a car bomb killed one man and injured at least 10 soldiers.
The blast, which blew out dozens of windows in nearby buildings, was set off by remote control in a working class suburb near a military academy.
Farc guerrillas launched a series of bombings that killed 21 people and injured 60 people when Mr Uribe first was elected president in 2002.
He won a second term in office in May.