Lagos - Three people have been charged in a Nigerian court with defrauding foreigners of over $2-million in a move which authorities said signals the start of a crackdown on a notorious international junk-mail scam.

The so-called "419" scam, named after the article in the country's criminal code outlawing it, has become so successful that campaigners say it is now the third to fifth largest foreign exchange earner in Nigeria, Africa's most populous nation.

Nuhu Ribadu, the chairperson of Nigeria's newly created Economic and Financial Crimes Commission (EFCC), told Reuters the court cases, which are being prosecuted by the EFCC, are only the beginning of its fight against the scam.

"We are trying to bring all of them to justice... including highly placed members of society," he said. "Some of them are outside the country. We will go after them. We want to see that there is no haven for them anywhere in the world."

Campaigners have for years accused Nigerian authorities of not doing enough to fight the 20-year-old con act, which has advanced from mass-mailing methods to junk e-mail distribution.

The scam swindles hundreds of millions of dollars every year from people across the world, who respond to junk e-mails promising them a share of non-existent fortunes.

The commission has arrested 20 people so far - including the three already charged - and investigations are being carried out overseas in cooperation with Interpol, he said.

One of the three charged was Nigerian businessman Fred Ajudua, who was arrested by the EFCC two weeks ago and accused of defrauding a Dutchman of $1,7-million.

"As far as we are concerned he does not know anything about this allegation," said Ajudua's lawyer, Olalekan Ojo.

An investigator from the commission said Ajudua had promised the Dutchman $36-million from Nigeria, which had supposedly been put aside by the aviation ministry after over-invoicing for a contract.

The Dutchman said in an affidavit seen by Reuters that he was asked to pay a series of bribes and fees in order to get the money transferred into his bank account, but the money never arrived.