The case has infuriated President Tayyip Erdogan and his ministers, some of whom accuse U.S. court officials of ties to a cleric blamed for a 2016 coup attempt. Some of the testimony at the trial implicated senior officials including Erdogan.
Mehmet Hakan Atilla, an executive at Turkey's majority state-owned Halkbank, was convicted on five of six counts in a Manhattan federal court on Wednesday, including bank fraud and conspiracy to violate U.S. sanctions law.
"It is an unjust and unfortunate development that Halkbank Deputy General Manager Mehmet Hakan Atilla was found guilty," Turkey's foreign ministry said in a statement.
"The U.S. court, in a process carried out by relying on so-called 'evidence', which is fake and open to political exploitation, ... made an unprecedented interference in Turkey's internal affairs."
Erdogan, who has yet to comment on the decision, has previously dismissed the trial as a politically motivated attack on his government, and attempted to use the case to tap into anti-American sentiment among nationalist supporters.
Ankara has not, however, threatened to take concrete measures.