MILAN (Reuters) - An Italian unit of Amazon ( AMZN ) is being investigated by Milan prosecutors for suspected tax evasion, two sources said on Friday, but the inquiry was not linked to a multi-million euro seizure from another of the group's Italian units this week.

Italy's tax police on Tuesday seized some 121 million euros ($131 million) from another unit of the U.S. e-retailer as part of an investigation into alleged tax fraud and illegal labour practices, prosecutors' documents showed.

The second tax evasion investigation started in 2021 and was triggered by routine checks carried out by tax police in an area north of Milan, the two sources with knowledge of the matter said.

The inquiry focuses on tax rules over the trading of goods within Italy's borders and internationally, with particular reference to value added taxes and custom duties, the sources said.

The size of the potential tax evasion has not yet been quantified, they said.

Amazon ( AMZN ) had no immediate comment.

Italy's tax authorities and tax police in the city of Monza, just north of Milan, have been conducting checks on Amazon ( AMZN ) accounts in Italy in relation to the inquiry over the past few years, they said.

($1 = 0.9211 euros)

(Reporting by Emilio Parodi; Additional reporting by Elvira Writing by Valentina Za; Editing by Ros Russell)