BOGOTA, COLOMBIA, OCT. 26 -- A new wave of killings and kidnappings that have rocked Colombia's three largest cities this week is part of a bitter and bloody war between leading cocaine cartels, authorities said today.

"This is the worst inter-cartel violence we have ever seen," said one intelligence official. "It looks as if the whole thing is going to explode."

The Cali and Medellin cocaine cartels, which together export 80 percent of the cocaine consumed in the United States and Europe, have fought over tactics, markets and personal rivalries in the past, but the number and brutality of the recent killings surprised many observers.

Recently, the Cali cartel, which traditionally has been less violent than its Medellin counterpart, has been growing rapidly, while the Medellin cartel has suffered setbacks at the hands of the authorities.

Two men and a woman from Medellin, apparently sent to Bogota to carry out an attack for the Medellin cartel, were found dead at a house in the capital Thursday night. The three were wrapped in mattresses, gagged and with their hands and feet bound. They had been tortured before being shot at least 15 times each, according to a police report.

Police said they found 147 sticks of dynamite in the house, along with a car with a special compartment, leading them to believe the three were planning some sort of terrorist attack.

According to neighbors, six assassins went to the house in a single vehicle. Inside the house, they spray-painted slogans such as: "Death to the Medellin cartel," "Here lie three killers from Medellin" and "War is war, and if you do not believe it look at the bodies."

At dawn Thursday, 12 men recently arrived from Cali were dragged from their rooms at a hotel in Medellin, authorities said. Today, four of the men were found shot to death at different points of the city, while eight remained missing. Two of the bodies had signs pinned to them reading: "Because they are from the Cali cartel. War is war."

Authorities said the current fighting between the cartels erupted Sept. 25, when 28 men of the Medellin cartel gunned down 19 persons on a farm 20 miles east of Cali. The owner of the property, Francisco Herrera, is a leading partner in the Cali syndicate and a bitter personal enemy of Medellin cartel leader Pablo Escobar, authorities said.

"It looks to us like Cali sent people to Medellin and Bogota to exact revenge, but the ones in Medellin got caught," said one European narcotics expert. "Everyone knew the Cali organization could not just let the killing of the 19 people pass. Now we can expect it to really get ugly."

"Colombia has lived through episodes of violence between the cartels in the past," said Gen. Miguel Maza Marquez, director of the Department of Administrative Security, Colombia's equivalent of the FBI. Speaking at a press conference today, Maza said his investigators "must wait a little longer before we can say with certainty what is happening."

Also Thursday, nine persons, including five children, were shot and stabbed to death by a group of armed men near the town of Tierralta, in Cordoba province. Three of the people were decapitated, police said. The motive was not immediately clear but the killings occured in an area where paramilitary groups, with strong ties to the Medellin cartel as well as sectors of the military, operate and have carried out a series of killings in recent months.