NEW YORK (AP) — Federal prosecutors asked a judge Wednesday to imprison a Turkish banker for over 15 years for helping Iran evade economic sanctions, saying he was a key player in undermining efforts to curb Iran’s nuclear ambitions.

The U.S. government said in papers filed in Manhattan federal court that Mehmet Hakan Atilla lied at a trial that ended in January as he tried to minimize his role in a multi-year scheme to launder billions of dollars in Iranian oil proceeds.

The prosecution further strained relations between the U.S. and Turkey.

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Atilla, 47, is scheduled to be sentenced next Wednesday after his conviction on multiple conspiracy charges and bank fraud. In papers filed last week, his lawyers sought leniency, saying even four years in prison would be too long a penalty for the deputy general manager of state-run Halkbank.

A spokesman for Turkish President Recep Tayyip Erdogan has called the trial outcome a “scandalous verdict.”

In their papers, prosecutors called Atilla’s crimes “without parallel” and said they provided Iran with a slush fund to use as it wished, damaging U.S. efforts to deprive Iran of money to pursue nuclear weapons.

They criticized Atilla’s pre-sentencing claims, saying he downplayed his crimes as he noted that he owes no allegiance to the U.S.

“This is a breathtaking minimization of a concerted, prolonged, willful effort to evade and subvert U.S. sanctions that were part of a highly public international effort to curb the nuclear ambitions of the world’s foremost state sponsor of terrorism and a leading threat to world peace and stability,” prosecutors said.

They added that Atilla had plenty of warning about his crimes because he regularly lied in person and by phone with senior U.S. government officials in Turkey and in the United States as he tried to shield his bank from sanctions against it.

“Whether Atilla owed any ‘allegiance’ to the United States lacks any sentencing significance,” the government said.

It said Atilla’s lawyers were seeking “extraordinary leniency” when they told the judge that Atilla was “at most, a functionary in someone else’s mammoth plot to circumvent American economic sanctions aimed at Iran.”

At trial, prosecutors said Atilla began in 2011 to conspire with Turkish gold trader Reza Zarrab to let Iran trade its oil and gas for gold, with some of the funds moving through U.S. financial institutions without their knowledge.

Zarrab pleaded guilty and testified against Atilla, saying he paid over $50 million in bribes to Turkey’s finance minister in 2012 to advance the scheme. He also testified that he believed Erdogan knew about the plot.

Atilla has remained incarcerated without bail.