Turkey yesterday condemned the US conviction of a Turkish banker for evading Iran sanctions as unprecedented meddling in its internal affairs, seeking to rally nationalist sentiment against a case that has implicated President Tayyip Erdogan.

Wednesday's court decision capped a trial that had strained diplomatic relations between the two countries and is likely to further aggravate tension between the Nato allies.

The case has angered Erdogan and his ministers, some of whom accuse US 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. Ankara has said the case was based on fabricated evidence.

Mehmet Hakan Atilla, an executive at Turkey's majority state-owned Halkbank, was convicted on five of six counts in a Manhattan federal court, including bank fraud and conspiracy to violate US sanctions law.

"The US 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," Turkey's foreign ministry said.

US prosecutors have charged a total of nine people in the case, including a former economy minister, Zafer Caglayan. However, only Atilla and a wealthy Turkish-Iranian gold trader, Reza Zarrab, are in US custody.

Erdogan, who has yet to comment on the decision, has previously dismissed the trial as a politically motivated attack on his government, and has attempted to use it to tap into anti-American sentiment among his supporters.

Ankara has not, however, threatened to take concrete measures.

The US case against Atilla was based on the testimony of the gold trader Zarrab, who cooperated with US prosecutors and pleaded guilty to charges of leading a scheme to evade US sanctions against Iran.

In his testimony Zarrab implicated top Turkish politicians, including Erdogan. Zarrab said Erdogan, who has governed Turkey for nearly 15 years, personally authorised two Turkish banks to join the scheme when he was prime minister.

"The Zarrab court case is a political plot", Deputy Prime Minister Bekir Bozdag tweeted yesterday.

Halkbank said Atilla had the right to appeal against the decision and said it had not been a party to the US case. It noted there had been no financial or administrative decision taken against it by the court.