LOS ANGELES (AP) _ A federal investigation touched off by the discovery of 20 tons of cocaine in a California warehouse has turned up drug-trafficking links in Nevada, Texas and Mexico.

Seven people were in custody in Los Angeles and Nevada in connection with the haul - the largest seizure in the world. Six warehouses in El Paso, Texas, as well as three homes across the border in Ciudad Juarez, Mexico, were raided by police, who said the facilities were used as stopovers by the suspected smugglers.

''We feel these warehouses were used as staging warehouses before the cocaine was sent to Los Angeles,'' said U.S. Drug Enforcement Administration special agent Phil Jordan.

Investigators said the cocaine entered the United States through El Paso before ending up in a San Fernando Valley warehouse operating as Adriana's Pottery Warehouse, where police and federal drug authorities made the record seizure Thursday.

The bust attracted so much attention that looters showed up at the unguarded warehouse and began to remove its remaining contents only hours after the cocaine was removed.

DEA agents said they secured the building, but the looters managed to gain entrance and snatch up Mexican pottery that was part of the company's merchandise.

No arrests were made, and police said nothing of evidentiary value was taken.

When drug enforcement agents across the country heard of the bust, possible connections to the smugglers began emerging.

One such link between the Los Angeles seizure and a house in Juarez was confirmed when one of the Los Angeles suspects telephoned the house from jail and a police officer there answered the phone, Jordan said.

No arrests were made, but a tractor and two trailers fitted with secret compartments were seized outside the house. ''In one of these compartments we found 500 pounds of marijuana,'' Jordan said.

El Paso DEA agents also found boxes similar to those found in the Los Angeles raid, along with Mexican pottery similar to that in that warehouse.

The four men being held in California have refused to give their names, saying only that they are from Mexico, police said.

Huntington Park police Sgt. Mike Leinen said the men were to be arraigned Monday on state charges.

The three men arrested Friday in Las Vegas were scheduled for arraignment Monday in U.S. District Court in Nevada.