A multi-million dollar fraud ring has been cracked in Nigeria's largest city, Lagos, say investigators from Nigeria, the United Kingdom and United States.
Western businesses are often targeted by Nigerian fraudsters
The crackdown on fraudsters using postal services saw 15,000 counterfeit cheques, written to the value of more than $4m (£2m), intercepted in a month.
Tonnes of mail were sifted to look for documents sent by "advance fee" conmen.
The discovery will pave the way for a major cross-border criminal investigation.
The so-called advance fee fraud involves sending people e-mails requesting their help in exporting a lump sum from Nigeria.
Victims are promised a share of the cash and asked for their bank details.
The anti-fraud police also found fraudulent identification papers and forged financial documents concealed in such a way as to prevent them from being picked up by security scanners.