Juan Pablo Escobar leaves court

Victoria Henao Vallejos and her son Juan Pablo Escobar were detained at their Buenos Aires apartment after local television blew the cover of a carefully planned police stakeout, officials said.

They appeared in court on Tuesday under heavy security, but no formal charges were brought against them. The judge warned more arrests would follow.

Pablo Escobar, who was shot dead in 1993, headed the notoriously violent Medellin cocaine cartel, which became one of the biggest cocaine suppliers to the United States.

His wife and two children are said to have a fortune worth more than $1 billion.

Escobar, his wife and son pictured at a soccer match

Investigators had secretly observed their apartment in the middle-class neighbourhood of Nunez for months as part of an investigation into money laundering in Argentina.

But Judge Gabriel Cavallo decided to order the Escobars' arrests just hours after a current affairs show revealed their presence in the country, Security Secretary Miguel Angel Toma said.

"We would probably have preferred to continue monitoring for a bit longer, but we had to act because of the possibility of a leak," he added.

Living in fear

Escobar was one of the world's most wanted men when he was killed six years ago in a rooftop shootout with police in Medellin, the city that gave his drug gang its name.

Victoria Henau Vallejos escorted by a body guard in Bogota

Since then, his widow and two children have lived in fear of revenge attacks by his enemies and of kidnapping by criminals envious of their wealth.

The family fled Colombia in 1995 for a new life abroad, after fruitlessly searching for a country to grant them asylum.

Juan Pablo Escobar, now 21, once even asked the Vatican to intervene to find them a place to live.

Officials said they had been living in Buenos Aires for nearly 18 months after entering the country through Chile with false documents.

Escobar's wife was living under the name Maria Isabel Santos Caballero and his son under the name Juan Sebastian Marroquin Santos. His daughter was not implicated in the case.

Money laundering

After hearing the news, Argentine President Carlos Menem said he was concerned drug traders could be pushing financial tentacles into his country.

"I think we will have to deepen the investigations, to find out if there is some drug-trafficking ring here, in Argentina - to find out if there are people involved here," he added.