The spokesman for Turkey's ruling AK Party said on Tuesday that if the United States designated the Muslim Brotherhood a foreign terrorist organization, it would hamper democratization efforts in the Middle East and serve militant groups like Islamic State.
The White House said on Tuesday President Donald Trump was working to declare the Muslim Brotherhood a foreign terrorist organisation, a step that would bring sanctions against Egypt's oldest Islamist movement.
Egyptian President Abdel Fattah el-Sissi asked Trump to make the designation, which Egypt has already done, in a private meeting during an April 9 visit to Washington, a senior U.S. official said, confirming a report in the New York Times.
Omer Celik, spokesman for Turkish President Tayyip Erdogan's Islamist-rooted AK Party, said such a decision by the United States would "undoubtedly yield extremely wrong results regarding stability, human rights, basic rights and freedoms in countries of the Islamic world," he said.
"At the same time, (Trump's move) is the biggest support that can be given to the propaganda of Daesh," he said, referring to Islamic State.
Despite being NATO allies, Turkey and the United States are currently at loggerheads mainly over their opposing interests in Syria and Ankara's plans to buy Russian missile defenses.
Relations between Ankara and Cairo have been strained since the Egyptian military, then led by Sissi, ousted President Mohamed Morsi, a senior figure in the Muslim Brotherhood, in 2013 after mass protests against his rule.
The Muslim Brotherhood has close ties with Turkey's AK Party and many of its members have fled there since its activities were banned in Egypt. It says it is an entirely peaceful organization.
Egypt's Brotherhood said on Tuesday it would continue to work in line with "our moderate and peaceful thinking" regardless of moves by the Trump administration.
Egyptian authorities under Sissi have jailed thousands of its followers and much of its leadership, including Morsi.
The Brotherhood says it is a non-violent movement and denies any relationship to violent insurgencies waged by al-Qaida and Islamic State militants.