Colombian police stand guard near the scene of the shooting
Colombia's fight against drugs involves different security forces
Colombian troops have accidentally shot dead 10 undercover police officers working on an anti-drugs operation in southern Colombia, officials say.
Soldiers near the town of Jamundi mistook the police for drug traffickers, Defence Minister Camilo Ospina said, announcing an inquiry.
A civilian was also killed in the skirmish, Mr Ospina said.
President Alvaro Uribe, who is standing for re-election on Sunday, urged a speedy and complete investigation.
"I regret to announce that an accident occurred that resulted in the death of 10 police officers and one civilian," Mr Ospina told a news conference in Bogota.
Police chief Jorge Daniel Castro said those killed were members of the judicial police working to dismantle a drug-trafficking group.
The town of Jamundi is in the Valle region, southwest of the capital, Bogota.
Drug traffickers and the Revolutionary Armed Forces of Colombia (Farc), the country's largest rebel group, are active in the region.
'Lack of consultation'
Various security forces in Colombia have their own units to combat drug-trafficking, kidnapping and extortion, and often keep their investigations secret to prevent leaks, correspondents say.
President Alvaro Uribe (right) greets supporters on the campaign trail on 22 May
President Uribe called for a swift inquiry
"There are many such different operations and obviously the different units don't consult with each other," Mr Ospina said.
The minister said a commission comprised of generals and the prosecutor's office would investigate what had happened, and that a team had already been sent to the scene.
The shooting comes less than a week before Colombia holds a presidential poll in which Presdient Uribe is seeking a second term.
Mr Uribe described the shooting as "extremely serious" and called on investigators to "quickly tell the country the whole truth so this doesn't turn into another Guaitarilla."
He was referring to a shootout in southern Colombia in March 2004 when seven police officers and four civilians were shot dead by soldiers.
The authorities were criticised for the slow pace of the investigations amid accusations of cover-ups by both the police and the military.
Mr Uribe, who is expected to win re-election, has won popular support for his hard line on crime and the country's insurgency but his critics say increased official pressure for results from the security forces have led to more shooting blunders.
Monday's shooting was the latest in a series of "friendly fire" incidents since 2004 that have left more than 30 soldiers, police and civilians dead.