MEDELLIN, Colombia (AP) _ A car bomb exploded early today in front of an apartment building owned by reputed cocaine baron Pablo Escobar Gaviria, killing two security guards and leaving a 16-foot-deep crater, officials said.

Five people in neighboring buildings were injured in the 5:15 a.m. explosion, which tore open water mains and caused damage as much as a half- mile away, police said.

Mayor William Jaramillo Gomez said the bombing of the six-story Monaco apartment building in the fashionable El Poblado neighborhood of this northwestern city was apparently aimed at Escobar.

Two different groups claiming to have launched a war on drug traffickers claimed responsibility for the bombing in telephone calls to the Colombian radio network RCN.

A few people were seen running from the building after the explosion, but it is not known who they were, said the chief of police, Col. Antonio Sanchez.

Escobar's wife and son live in the building. Escobar, who is wanted for extradition to the United States, has been in hiding for two years, but Jaramillo said he has often been seen at the building.

The Escobar family lived in one apartment. The others were filled with art works and antique and new cars and motorcycles, said Jaramillo's wife, Luz Elena de Jaramillo.

U.S. authorities say Escobar heads the Medellin Cartel, which it blames for as much as 80 percent of all the cocaine entering the United States.

''This looks like Beirut and it's a warning of where the violence that afflicts can bring us,'' said Jaramillo. ''There is no precedent in Colombia for an attempt of this magnitude. The car-bomb was reduced to thousands of little pieces.''

The blast, which left a hole 25 feet wide, destroyed or heavily damaged several homes, he said. Engineers estimated the damage at $7.5 million.

Sanchez said the bombing could be part of a new episode in fighting between drug traffickers in which 10 people have been shot dead since Saturday.

An anoynymous caller to RCN claimed the bombing was the work of a group calling itself Death to Drug Traffickers, a previously unheard of group.

Another such caller to RCN said the National Socialist Workers' and Students' Movement was responsible. That group has claimed last November for a machine gun attack on a communist youth headquarters in Medellin that left five people dead.

That group had said previously that it had set out to kill communists and drug traffickers.