Five people have been arrested in a nationwide investigation into fake marriages, the public prosecution department said on Wednesday.

In addition, officials are investigating 42 cases to determine whether residency permits can be withdrawn because the marriage was not genuine.

The investigation involved police, immigration officials, local councils and government ministry inspectors. Identifying marriages of convenience is key part of the crackdown on illegal immigration, the prosecution department said in a statement.

In addition, fake marriages often involve human trafficking and other criminal activities, the statement said.

In 2014, some 200 requests for residency permits in the Netherlands were rejected because officials said the marriages were not genuine.

Earlier this year, MPs from the Liberal democratic party D66 said they were concerned the tough rules on bringing foreign partners to the Netherlands – which are aimed at stopping fake marriages – were hitting returning Dutch expats.