The trial is set to begin against a Turkish employee of the U.S. Consulate in Istanbul charged with espionage and attempting to overthrow the Turkish government.

Metin Topuz, a translator and fixer for the Drug Enforcement Agency at the consulate, will have his first hearing Tuesday. He has been in pretrial detention since October 2017.

Topuz is accused of links to U.S.-based Turkish cleric Fethullah Gulen, who the Turkish government blames for the 2016 coup attempt. He denies the allegations.

Topuz's arrest led to the suspension of bilateral visa services for more than two months in 2017 and is one of several contentious issues increasing tensions between the two NATO allies.

The first hearing in Istanbul is expected to continue until Thursday.