ISTANBUL (AP) — A Turkish employee of the U.S. Consulate in Istanbul appeared in court Tuesday charged with espionage and attempting to overthrow the Turkish government in a case that further frayed ties between the two NATO allies.

The trial against Metin Topuz, a translator and fixer for the Drug Enforcement Agency at the consulate, opened in Istanbul nearly a year and a half after his arrest in October 2017. He has been held in pre-trial detention since then.

Topuz is accused of links to U.S.-based Turkish cleric Fethullah Gulen, who the Turkish government blames for the 2016 coup attempt, and faces a life sentence if convicted. Topuz, 59, denies the allegations.

"I would never have thought I'd be blamed for my translation work," Topuz said, fighting back tears.

Topuz's arrest led to the suspension of bilateral visa services between the U.S. and Turkey for more than two months in 2017 and is one of several contentious issues that have increased tensions between Ankara and Washington.

In the 78-page indictment, Topuz is accused of links to officers who led a 2013 corruption investigation that implicated top Turkish officials. 

The Turkish government accuses those officers of links to Gulen and of attempting a "judicial coup" through the investigation. Among the 30 complainants against Topuz are Turkish President Recep Tayyip Erdogan and former ministers. 

"During my 25 years of work with the DEA, I have met many police officers and public officials, exchanging numbers and business cards," Topuz said in his trial testimony.

Topuz began working at the consulate in 1982 as a switchboard operator and was promoted to work as an assistant and translator to the DEA's American personnel in Turkey a decade later.

He explained that his work for the DEA involved contacts with Turkish security forces, especially narcotic officers, in drug-related investigations and informational exchanges on combatting drug use. Topuz said he was also involved in security preparations during visits by U.S. presidents.  

Topuz argued that the prosecutor only took into account contacts he had with officers allegedly linked to Gulen and ignored conversations he had with hundreds of other officers.

Topuz said he communicated with public employees of the Turkish state and cannot be expected to know or identify officers with alleged links to Gulen.

The indictment includes telephone calls, text messages, CCTV frame grabs with suspected police officers, along with testimonies from four witnesses and two suspects.

He's also accused of privacy violations and illegally recording personal data.

Speaking to journalists before the trial, Topuz's lawyer, Halit Akalp, said the defense team would request his release.

"Our expectation is Mr. Topuz's release," the lawyer said.

Once an ally, the Turkish government declared Gulen and his network a terror group in 2014 following the anti-corruption investigations. Tens of thousands of police officers have been dismissed and many were arrested for alleged links. 

Turkey is demanding that the U.S. extradites Gulen, who lives in the Pocono mountains in Pennsylvania.

U.S. diplomats, including Charges d'Affaires Jeffrey Hovenier and Istanbul Consul General Jennifer Davis, were attending the three-day hearing.

The first hearing is expected to continue until Thursday.

Associated Press writer Suzan Fraser in Ankara, Turkey contributed.