Police say they have broken up an international cartel that allegedly exploited boxers, forcing them to fight against their will in competitions right across Europe.

A three-month investigation has resulted in the arrest of seven Spanish nationals suspected of belonging to the ring.

They are being held accused of fraud, forgery, making threats and causing bodily harm.

Spanish officers say they have released 19 'victims' who were made "without undergoing medical controls and with false permits and licences".

The group, based in the industrial town of Terrassa, north of Barcelona, allegedly used a former Nicaraguan boxer dubbed 'El Terrible' to make contact with, and recruit, the victims.

A sports event company would invite the boxers to Spain to take part in a fight and once they arrived in the country the ring would hold them in a home in "overcrowded and unhealthy conditions", a police statement said.

"If they did not obey orders, members of the group would hit them and threaten to hurt their family members back in Nicaragua," the statement added.

The money earned from these fights would go entirely to the cartel.

The suspects have all been arrested over the past few weeks, a police spokesperson confirmed.