Nineteen people have been arrested across England and Northern Ireland as part of an investigation into a series of raids on museum and auction houses.
Fourteen men and two women were arrested in England, while three men were detained in Northern Ireland.
Officers from the Criminal Assets Bureau also carried out a number of searches in counties Limerick and Cork as part of an ongoing Europol initiative.
A number of artefacts, cash and a large quantity of documentation were seized in the operation, which targeted residences in Rathkeale and Raheen in Limerick and Newmarket in Co Cork.
The people arrested in the UK and Northern Ireland are being held on suspicion of conspiracy to burgle, apart from a 54-year-old woman, who was arrested on suspicion of perverting the course of justice and assisting an offender.
The investigation is connected to six crimes over a four-month period at museums and auction houses across England.
Chinese artefacts and rhinoceros horns were stolen from Durham Museum, Gorringes Auction House in East Sussex, Norwich Castle Museum in Norfolk and the Fitzwilliam Museum in Cambridge.
While much of the property was subsequently recovered, several high-value items are still missing.
The value of the stolen property is believed to be over €40 million.
The Europol initiative was set up in 2010 to target the activities of an international criminal group, including labour exploitation, counterfeiting, tobacco smuggling and tarmac scams.