SAO PAULO - A plot to smuggle cellular phones into a prison yard using a remote-control model helicopter has been foiled after Brazilian police discovered the high-tech toy in the trunk of a car outside a maximum-security lockup.

Police say they confiscated the one-metre-long chopper near the Presidente Venceslau penitentiary in Sao Paulo state and arrested four people riding in the car.

Attached to the helicopter's base was a basket-like container with nine cellphones wrapped in a disposable diaper, a police statement said.

Another five cellphones were found inside the car trunk.

Police Sgt. Ricardo Jock told the Globo TV network: "The cellphones were obviously for jailed gang leaders who would use them to co-ordinate bank robberies and kidnappings and set up drug deals."

In March, police thwarted an attempt at using carrier pigeons to fly cellphones into a prison near the southeastern city of Sorocaba.

In that case, guards spotted a pigeon resting on an electric wire with a small cloth bag tied to one of its legs. Luring the bird down with food, they discovered components of a small cellphone inside the bag.

Police said one of the suspects arrested on Sunday acknowledged receiving about US$5,000 to buy and prepare the helicopter, and that he would have received the same amount again for successfully landing it inside the prison.

Imprisoned Brazilian gangsters use cellphones to co-ordinate criminal activity outside and inside an overcrowded prison system where torture, killings and gang violence are routine.

In 2006, Sao Paulo's notorious First Capital Command gang - whose leaders are based in prison - used cellphones to launch a wave of assaults on police, banks and buses that left more than 200 people dead in South America's largest city.