BOGOTA - A bomb exploded in a crowded area of Bogota Tuesday, killing five people in what Colombian President Juan Manuel Santos said was an attempt to assassinate a former interior minister.

"I've just learned that an attempt was made on the life of Mr. Fernando Londono. He was in his armoured car," said Santos in a speech from the presidential palace. Santos said Londono's driver and a police guard were killed in the blast which ripped through an area of northwestern Bogota that is normally crowded with pedestrians from nearby office buildings and universities.

"Fortunately, Dr London is stable condition in the hospital," Santos said. Londono was interior minister under former president Alvaro Uribe, a hardliner who governed from 2002 to 2010. The Red Cross said five people were killed in the explosion, and 17 others were injured.

The attack came shortly after the police announced they had dismantled a car-bomb that leftist FARC rebels planned to use in an attack on the Bogota police headquarters.

Witnesses said the blast, which occurred just after 11:00 am (1600 GMT), appeared to have been from a bomb placed on a public bus, but officials could not immediately confirm that.

Television stations aired images of the scene that showed a green van with the roof blown open.

Half a dozen vehicles were incinerated in the explosion, AFP journalists on the scene said.

"I want to condemn this attack in the strongest terms," said Santos. "We do not know what the purpose of it was, but be absolutely certain that the government is not going to allow itself to be derailed by these terrorist acts."

The last car bomb to explode in the Colombian capital was on August 12, 2010, two days after Santos was inaugurated.

That attack, which injured nine people, was blamed on the Revolutionary Armed Forces of Colombia (FARC), the country's biggest leftist guerrilla group with an estimated 9,200 fighters.