The gangs are mostly run by Nigerians pretending to be businessmen who court their victims with promises of love, friendship, free holidays or cash rewards, according to Singapore's drugs police.

In return, the Singaporean women would fly to a designated country to collect the drugs and deliver them to another place, the Central Narcotics Bureau (CNB) said in a statement.

"CNB has been watching for the presence of these syndicates and monitored them closely when these cases surfaced," a statement from the agency said.

Investigations showed the conmen "befriended the Singaporean couriers at public places or through social networking websites".

"Many of these female Singaporean drug couriers were cajoled into carrying out the drug runs with promises of love and friendship or inducement of free holidays or cash payment."