Collaboration between Nigerian organised crime and the Sicily-based mafia syndicate Cosa Nostra is increasing in the Sicilian capital of Palermo in spite of a recent crackdown by authorities.

The Vikings, a gang that originated in Nigeria in the 1980s, is now controlling heroin and prostitution rackets in the Ballaro' neighbourhood. It is particularly benefiting from the trafficking of thousands of Nigerian women who, once their reach Italy, are forced into prostitution.

Authorities believe the Vikings are working alongside Cosa Nostra, "This Thing of Ours", probably the oldest crime syndicate in Italy and one of the world's major drug-smuggling players.

"There is harmony in Ballaro'. Nigerian lookouts posted to watch for the police will alert Cosa Nostra members as well as their own," a police source told The Times.

However, the source added the status quo is precarious.

"If we weaken the Italians, the Nigerians may start to operate outside their own communities, just as the north Africans are now doing in Naples," the source said.

The Vikings, whose members wear red berets and have a secret handshake, originated as a lobby group in Nigerian universities in the 1980s.

The emergence of the Vikings in Ballaro' comes months after a crackdown by Sicilian police on its rival gang, the Black Axe , which also orientated as a fraternity group in Nigeria in the 1970s.

In November 2016, Sicilian police arrested at least 20 members of the Black Axe, known for its use of machetes instead of conventional weapons and the practice of voodoo to intimidate African women and keep them in the prostitution racket.

The crackdown took place after a machete-wielding Black Axe member, understood to be the group's "minister of defence" attacked a member of the Vikings in Ballaro'.

In spite of the fact that several arrests were made, Ballaro' is now seeing the emergence of the Vikings.

"When you take out one, others will try to fill the gap," explained Rodolfo Ruperti, head of the Palermo flying squad.

The Black Axe gang has been linked to high levels of migration into Italy from North Africa.

"The Black Axe are very hierarchical, with bosses from each town, a boss for Italy and meetings to elect a European boss," the police source said.

On the contrary, not much is known about the structure of the Vikings.

"We don't know if the Vikings have a national boss," the source said. "They are less structured, with less of a code".

The source further explained that while Nigerian gangs might use "primordial violence" against each other, they won't do so against the Italian Mafia, and this could explain the current harmony with Cosa Nostra.

The police officer also said that a lack of interpreters who can translate wire taps is slowing investigations into the extent of the Nigerian gang-related crime in Sicily.

However, the source added that following the November 2016 crackdown "more Nigerians stepping forward to denounce the mobs.

"We will make it harder for whoever tries to take over," the source concluded.