Washington on Sunday denounced as “regrettable” France’s decision to free an Iranian engineer threatened with extradition to the US in exchange for a French researcher.

“The US deeply regrets France’s decision to release Iranian national Jalal Rohollahnejad from its custody,” US Department of State spokeswoman Morgan Ortagus said in a statement.

French researcher Roland Marchal returned to Paris on Saturday after being imprisoned in Iran for more than nine months.

Earlier, President Emmanuel Macron announced that Tehran freed Marchal after France released Iranian engineer Jallal Rohollahnejad, who is accused in the US of violating sanctions placed on the country.

“The United States and France have a shared interest in bringing those accused of serious crimes to justice, particularly in cases with national security implications,” Ortagus said.

“It is regrettable in this instance that France failed to uphold its treaty obligations and prevented justice from being pursued,” she said.

Rohollahnejad stood accused in the US of trying to smuggle technological material into Iran in violation of US sanctions.