Last year, Washington announced sanctions against buyers of Iranian oil, granting eight countries, including Turkey, waivers for six months. It said on Monday it will not renew those waivers and demanded that buyers stop purchases by May 1 or face sanctions, according to Reuters.

Iran is one of the biggest oil suppliers for Turkey, which is almost completely reliant on imports to meet its energy needs.

The US decision damages regional cooperation and Turkey’s trade relations, Aksoy said during a press conference on Friday.

“Tupras is following the subject closely. The characteristics of their refineries are suitable for Iranian oil. We are trying to convince the US,” he said, responding to a question about whether the refiner will continue buying crude oil from Iran.

Ties between the NATO allies have been strained lately over Turkey’s push to purchase Russian S-400 missile systems, which Washington says could compromise its F-35 fighter jets, and over differences in policy in Syria.

Ankara has proposed the creation of a working group to assess the impact of the S-400 on NATO systems. The United States has not yet responded to that proposal, Aksoy said on Friday.

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