Security experts are concerned that the 3in-long weapon, which contains two bullets and can kill from close range, could easily get past Customs officers unnoticed.
The gun, which is understood to have been made in Bulgaria, is believed to be used by organised crime gangs who can smuggle it across borders without detection, but there are fears that it could also be taken on to aircraft by hijackers.
The weapon costs about pounds 14 and cannot be detected by some traditional metal detectors and airport X-ray machines.
The Interpol bureau at the National Criminal Intelligence Service in London issued the warning to 177 countries after the device was found at Heathrow at the beginning of the year.
A similar weapon was seized in Athens last Wednesday after it had passed through an X-ray machine undetected. Guns were also found at Perth airport in Australia and Athens last September.
Although the device is made of metal it is likely to pass through airport security checks because passengers usually put key rings, coins and other metal objects on a tray that is passed around the detector. The mini-gun can thus be camouflaged by harmless objects.
The gun is intended to fire cartridges filled with gas to ward off attackers, but it can also take .32 calibre bullets and has a range of about seven metres. The trigger itself is disguised as the key ring.
There is no evidence to suggest that the weapon is available in Britain yet.Reuse content