Trafficking gangs are flourishing across Africa through the exploitation of hundreds of thousands of migrants, yet nations are failing to dismantle networks due to a lack of coordination, the United Nations said on Monday.

More than 800,000 people are trafficked across international borders annually - often duped with promises of a better life overseas, then sold into forced labour, domestic servitude or sexual slavery, according to the U.N.

Many victims are migrants from African nations such as Eritrea and Somalia, yet countries are failing to curb the crime as they lack mechanisms to share cross-border intelligence and coordinate efforts to bust trafficking rings.

“International cooperation has to get stronger and stronger,” said Amado Philip de Andres, Head of the U.N. Office on Drugs and Crime (UNODC) in Eastern Africa.

“I am referring specifically to international police and judicial cooperation to dismantle criminal networks involved in human trafficking.”

“Effective anti-human trafficking responses require strengthening coordination and cooperation between all nations - whether the country of origin, transit or destination,” he said at an event marking World Day against Trafficking in Persons.

At least 40 million people globally are estimated to be trapped in modern slavery as poverty, conflict and natural disaster fuel the growing global trade.

From men forced to work in factories, farms and on fishing boats and women made to sell sex to people exploited for their organs and children sent to beg, human trafficking is one of the fastest-growing criminal enterprises.

The eastern African region - located at the centre of traditional routes taken by migrants to get to Europe, the Middle East, the Gulf and South Africa - is particularly prone to traffickers who prey on vulnerable people, said experts.

Libya is the main departure point for African migrants attempting to reach Europe by sea, with more than 600,000 migrants crossing the Mediterranean to Italy over four years.

Trafficking and smuggling networks have flourished in Libya due political turmoil and armed conflict, with groups often profiting from multiple types of smuggling to Europe, from fuel and weapons to drugs and migrants.

These migrants are often subjected to torture, extortion and trafficking for organ removal. Armed groups also traffick them to the territories where they operate for sexual slavery, and force men and boys to become combatants.

Yet even if suspects are apprehended and victims rescued in one country, it is rare the bigger network of traffickers involved, including the king-pin who is in another country, are fully investigated and prosecuted, said experts.

Police investigators, prosecutors, magistrates require training and resources to be able to follow up on cases and a mechanism established for agencies to share information on victims, witnesses and suspects to ensure convictions.

Ethiopia’s ambassador to Kenya Dina Mufti said his country has taken steps to curb the crime - from passing anti-trafficking laws to police training on the new legislation.

This resulted in 640 trafficking convictions in 2016, up almost 90 percent from 69 convictions the year before, said Mufti, adding that there was a need to do more.

“Financial and capacity constraints, poor coordination between regions, the federal government and neighbouring countries are further hindering law enforcement efforts in the overall attempt to end trafficking,” he said.