Turkey dismissed Thursday a U.S. court conviction of a Turkish banker in connection with a billion-dollar plot to evade U.S. sanctions against Iran.

The court in New York City convicted Mehmet Hakan Atilla on four counts of conspiracy, including conspiracy to defraud the United States, plus one count of bank fraud. The 47-year-old Turkish national was acquitted on a charge of money laundering.

The Turkish Foreign Ministry said Thursday the ruling was unfair and unfortunate, and also an unprecedented interference in Turkey’s internal affairs.

Deputy Prime Minister Bekir Bozdag said on Twitter the jury’s decision does not carry legal value in Turkey.

The case has strained relations between Turkey and the United States.

Atilla is a deputy general manager at Turkey’s state-run Halkbank. U.S. prosecutors charged him with helping to facilitate a deal in which Iran traded oil and gas for gold, moving some of the transactions through U.S. banks without their knowledge.

Atilla was heard on telephone recordings setting up fake food and agriculture deals with Iran to disguise deals that were really sales of oil. Atilla’s lawyer said his client was merely “a hapless pawn” in those deals, blaming Atilla’s boss, Reza Zarrab, instead. 

Zarrab, a Turkish-Iranian trader who has admitted arranging the deals, told the court he paid about $50 million in bribes in 2012 to the Turkish finance minister to push the deals through. Zarrab testified that he believed Turkish President Recep Tayyip Erdogan was aware of the scheme.

Erdogan said the case is an American conspiracy to blackmail Turkey, a strategic partner with the United States in Middle East affairs.

Iran and the United States have had chilly relations since the Iran hostage crisis from 1979-1981, in which 52 Americans were held by student activists in Iran for 444 days until a release was negotiated. The United States now bans most financial dealings with Iran, which is a major oil-producing nation.