Russian crime gangs on the Costa del Sol are injecting kidnap victims with what they claim is an experimental KGB virus to terrify them into paying ransoms.

In the latest case, four Russians told their victim that he would die within 24 hours if he did not pay them €12,000 (£10,000). But the businessman called their bluff and alerted the police, who arrested the gang.

The kidnappers had seized the Russian businessman in the middle of a street last week in Estepona, a Spanish resort popular with British tourists and expatriates.

They put a hood over his head and bundled him into a waiting car. After being held for two days, during which he was subjected to threats, beatings and electric shocks, he was injected with a substance which the gang claimed was an experimental virus developed by the KGB, the former Russian security service.

The man was told that he would develop a fever, start sweating profusely, feel sick, then begin vomiting. Soon afterwards, they said, he would die.

The businessman did start sweating and feeling sick, and the gang tried to convice him that the only way they could save him was by injecting an antidote which they possessed. When they took him to get the cash from a bank they let him slip away, believing that he would return with the money. Instead, heavily armed police surrounded them.

The Spanish Organised Crime Unit arrested three men and a woman. All were Russian nationals aged between 24 and 57 and they have been charged with kidnapping, torture and possession of illegal fire arms.

Police seized a mobile phone from one kidnapper, in which he had photographed the way the gang tortured the victim.

Officers said that there had been a spate of kidnappings in this part of the Costa del Sol. In March, the wife and daughter of a Russian businessman were kidnapped in Estepona. The gang threatened to kill them unless the husband paid a €2 million (£1.7 million) ransom, but they were rescued within 24 hours.

The Russian mafia has been gaining ground in Spain since the decade-long property boom allowed many gangs an easy outlet to launder money. But police operations have detained two leading members of Russian crime cartels in the past 12 months.

Last year, Gennadios Petrov, the head of the Tambovskaya-Malyshevkaya gang, was arrested at his neo-classical mansion in Calvi, one of the most exclusive villages in Majorca. In a major operation, codenamed Troika, 20 alleged members of the organised crime organisation said to have been led by Petrov were arrested in Majorca, Málaga, Alicante, Valencia and Madrid. Police seized 23 luxury cars including Bentleys and Ferraris and €200,000 (£170,000) in cash.

Last weekend, Tariel Oniani, a Georgian considered to be the No2 in the Russian criminal empire in Spain, was arrested in Moscow.

In 2005, Oniani fled his mansion near Barcelona after a tip-off from a corrupt Spanish official on the eve of a major police operation against Russian crime gangs. He is expected to face charges of laundering illicit cash obtained from criminal activities in Russia into property, restaurants and car sales in Spain.

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