WASHINGTON/ISTANBUL (Reuters) - Turkey has indicted a third U.S. Consulate employee and his wife and daughter on charges of membership of a terrorist group, according to a copy of the indictment seen by Reuters, a move likely to further strain ties between Ankara and Washington.

U.S. Consulate is pictured in Istanbul, Turkey, October 11, 2017. REUTERS/Murad Sezer

Nazmi Mete Canturk, a security officer at the U.S. Consulate in Istanbul, and his wife and daughter are accused in the indictment of links to the network of Fethullah Gulen, the U.S.-based Muslim cleric blamed by Ankara for a failed 2016 coup.

A Turkish prosecutor is seeking jail sentences for all three on charges of membership of an armed terrorist organization, according to the indictment, which was completed on March 8 but has not been made public.

It says Canturk was in contact with dozens of individuals under investigation for being members of Gulen’s network and that “evidence has been obtained regarding the suspect’s actions in line with the instructions of the (terrorist) organization”.

Canturk, his wife and daughter are cited in the indictment as denying the charges.

A spokesman for the Istanbul prosecutor’s office did not respond to a request for comment. A lawyer for Canturk declined to comment. The U.S. Consulate referred questions to Washington.

A State Department spokeswoman said Washington had seen no credible evidence that Canturk was involved in any illegal activities and that, in his 30-year career, he had had many contacts with Turkish government and security officials in the course of his work. She called for a timely, transparent, and fair resolution of his case.

She added that the United States has raised Canturk’s case with the Turkish government. “We have expressed our concerns on multiple occasions to the Turkish government at the highest levels publicly and privately,” she said.

Canturk was questioned by Istanbul police in January 2018 and subsequently put under house arrest, according to the indictment and a preliminary proceedings report seen by Reuters. That report, dated March 22, said that his first hearing would be held on June 25.

Two other locally employed U.S. Consulate workers, also Turkish citizens, were arrested in 2017 on terrorism and espionage charges. The detentions prompted Washington to suspend non-immigrant visa applications from the country, triggering a reciprocal move from Ankara which snowballed into one of the worst crises between the two NATO allies.

A Turkish court ruled on March 28 that one of them, Metin Topuz, a translator and fixer for the Drug Enforcement Agency (DEA) at the U.S. consulate in Istanbul, should remain in jail until his trial resumes on May 15. If convicted, Topuz could face a sentence of life in prison.

The other, Hamza Ulucay, who worked as a translator at the U.S. Consulate in the southern city of Adana, was sentenced to four-and-a-half years in prison on terrorism charges but was released in January, with travel restrictions, after almost two years in detention.

Topuz has denied charges of espionage and links to Gulen. Ulucay also denied any links to terrorist organizations during his trial.

Earlier this month, two U.S. senators introduced a bipartisan bill requiring the imposition of sanctions on Turkish officials responsible for the detentions of U.S. citizens and local consulate staff.

In a meeting with Turkish Foreign Minister Mevlut Cavusoglu earlier this month, U.S. Secretary of State Mike Pompeo also called for the swift resolution of the remaining cases, the State Department said. Despite being NATO allies, Washington and Ankara are already at loggerheads over their opposing interests in Syria and Ankara’s plans to buy Russian missile defenses.