AMSTERDAM (Reuters) - Turkey is compromising the judicial independence of a United Nations war crimes tribunal by holding one of its judges in detention despite an order to release him, the court ruled, referring the matter to the U.N. Security Council.

The U.N. court had earlier ordered Ankara to release Judge Aydin Sefa Akay, a Turkish national who was detained last year on suspicion of involvement in last July’s failed coup, which claimed some 240 lives. [nL5N1FL4LT]

Akay, a judge on the Mechanism for the International Criminal Tribunals (MICT), had been due to hear a request to reopen the case of a Rwandan genocide convict when he became one of around 40,000 people to be detained in connection with the coup.

“Turkey’s non-compliance materially impedes the Appeals Chamber’s consideration of the merits of this case and threatens the independence of the Mechanism’s judiciary,” court president Theodor Meron said in a written ruling published on Monday.

The court, which is based in The Hague, said it had been unable to reach Akay.

The successor to tribunals that tried crimes committed during the Yugoslav wars and the Rwandan genocide, the court has no enforcement powers of its own. The U.N. Security Council can decide to pressure Turkey diplomatically or via sanctions or even force, though it very rarely acts in such cases.

MESSAGING APP

Turkish media reported that Akay had been arrested for having a messaging application on his phone that was allegedly used by many of the plotters in the coup, blamed by authorities on followers of exiled Muslim cleric Fethullah Gulen.

Turkey was a strong early backer of the international courts set up in the 1990s to try mass crimes from the Yugoslav wars and the Rwandan genocide, but it has taken a more unilaterally nationalist stance under President Recep Tayyip Erdogan.

Critics of Erdogan say he is using a crackdown on suspected supporters of the failed coup as an excuse to purge political rivals, a charge he denies.

Gulen, who lives in the United States, has condemned the coup and denied any involvement.

Akay had been due to hear pleas from lawyers for Rwandan politician Augustin Ngirabatware, now serving 30 years for inciting genocide. The lawyers say they have turned up exonerating evidence that merits a review of his case.

The proceedings are currently frozen.