THE HAGUE (AFP) - Dutch prosecutors Friday announced a criminal probe into Uber, in the latest salvo of an increasingly bitter battle between European governments and the popular taxi service app.

The move comes after a Dutch judge convicted three taxi drivers belonging to Uber's low-cost service UberPOP of ferrying passengers without a permit and slapping each with a €1,500 (S$2,000) fine.

"Uber is now a suspect in light of the judge's verdict," the Public Prosecutor's office announced in a statement.

"This means launching a preliminary investigation to gather detail to determine whether Uber is guilty of commercial organisation of illegal passenger transport," the statement added.

Dutch judges in December banned UberPOP from taking bookings via its smartphone app, threatening the US company with fines of up to €100,000.

Uber said it would contest the ruling and continued to offer UberPOP.

The Dutch government has since handed more than €50,000 in fines against Uber, Dutch media reported on Friday.

Uber uses mobile phone apps to put customers in touch with private drivers who then take them where they want to go, at prices lower than those of traditional taxis.

But despite its growing popularity, Uber is facing increasing limits on its activities in EU countries and a barrage of legal challenges spurred on by a furious taxi lobby, who say Uber drivers should be regulated the same way as normal cabs.

Uber earlier this month filed complaints with the European Union against France, Germany and Spain, hitting back at efforts to ban it from the continent's streets.

Uber said efforts by national governments to shut it down breached EU laws on competition and the single market.

If Brussels finds EU rules have been violated, it can launch in-depth investigations that could ultimately bring penalties and fines against the national governments.