ANKARA (Reuters) - President Tayyip Erdogan’s spokesman said on Wednesday the U.S. judge hearing the trial of an executive at Turkey’s state-owned Halkbank had taken part in events organized by a cleric Ankara blames for last year’s failed military coup.

“The issue has gone beyond a legal case, it has become a political case,” spokesman Ibrahim Kalin said in reference to the New York trial of a deputy general manager at the bank, who is charged with helping Iran evade U.S. sanctions.

The executive has pleaded not guilty and Halkbank says it has abided by Turkish and international law.

Erdogan’s government has portrayed the case as a “plot against Turkey” by the network of U.S.-based cleric Fethullah Gulen, who it alleges engineered last year’s coup attempt.

“It is known that the judge has participated in events upon Gulen’s invitation,” Kalin told a news conference, without giving details. Turkish newspapers have said Judge Richard Berman attended a legal symposium in Istanbul in 2014 organized by Gulen supporters.

Berman could not be reached for comment. At the first hearing in the case he said he was one of five U.S. legal experts who spoke at the symposium and moderated a panel discussion on independent and effective judiciary.

In response to previous criticism from Turkey, the United States has said its judicial processes are independent.

Already strained ties between NATO allies Ankara and Washington have deteriorated further over the court case, in which Turkish-Iranian gold trader Reza Zarrab, who is cooperating with U.S. prosecutors, has detailed a scheme to evade U.S. sanctions.

Zarrab has implicated top Turkish politicians, including Erdogan. Zarrab said on Thursday that when Erdogan was prime minister he had authorized a transaction to help Iran evade U.S. sanctions.

Although he has not yet responded to the courtroom claims, Erdogan has dismissed the case as a politically motivated attempt, led by Gulen, to bring down the Turkish government.

“We will continue watching it within the framework of the law, but the public is seeing how this is trying to be used as an instrument of blackmail,” Kalin said.

“We have not done anything in violation of international laws, we carried out our activities transparently,” Kalin said.

Turkey has repeatedly requested Gulen’s extradition, but U.S. officials have said the courts require sufficient evidence before they can extradite the elderly cleric, who has denied any involvement in the coup.

Gulen has lived in self-imposed exile in Pennsylvania since 1999.