Ten suspects and four companies were investigated for a "serious criminal offence against the environment, document forging, tax evasion and money laundering, all within a criminal association", the Office for the Suppression of Corruption and Organised Crime (USKOK) said.

The 10 were arrested on Thursday in the capital Zagreb and several other towns, it said.

The suspects are believed of having illegally disposed of more than 35,000 tonnes of waste at several sites in Croatia, police official Ivica Kropek told a press conference.

The alleged crimes occurred between 2022 and 2024, Kropek said.

The suspects are thought to have imported plastic waste from other EU countries and taken in medical waste from Croatia.

It was later buried in the ground or dumped.

USKOK said the dumping had caused "significant ecological damage" in Croatia that would be costly to put right.

Separately, European law enforcement agency Europol said Croatian authorities had arrested "13 people suspected of being part of an environmental crime network".

The two main suspects are believed to "have orchestrated the illegal import of hazardous waste from Italy, Slovenia and Germany to Croatia", it said.

An investigation showed that at least 35,000 tonnes of waste had been illegally disposed of at least three locations and the suspects had pocketed at least four million euros ($4.2 million).