U.S. President Donald J. Trump has become 1st Western leader to congratulate President Recep Tayyip Erdogan over his victory in Sunday’s referendum that significantly expanded presidential power.

White House said in a statement late on Monday that Mr. Trump spoke with his Turkish counterpart to “congratulate him on his recent referendum victory” and to discuss the U.S. action in response to the Syrian regime’s use of chemical weapons on April 4th.

The readout said President Trump thanked Mr. Erdogan for supporting this action by the U.S., and the leaders agreed on the importance of holding Syrian President Bashar al-Assad accountable. President Trump and President Erdogan also discussed the counter-ISIS campaign and the need to cooperate against all groups that use terrorism to achieve their ends.

“President Trump and President Erdogan also discussed the counter-ISIS campaign and the need to cooperate against all groups that use terrorism to achieve their ends,” the White House statement said.

In a historic vote on Sunday, only a slight majority of voters granted Mr. Erdogan sweeping new powers that would unwind century-old political system while opposition outcried fraud and widespread irregularities, contesting the result.

The referendum on Sunday effectively changed Turkey’s political system, transferring the center of power from Parliament to the Presidency. Mr. Erdogan will now have powers such as dissolving Parliament, bypassing Parliament through executive decrees and declaring the state of emergency. The constitutional changes also significantly weakened checks and balances and gave the president a greater control over the judiciary.

No Western leader congratulated President Erdogan as of Monday, breaking a long tradition in a sign that they are not pleased with the outcome. Some Western governments said they would make a statement after international observers announce their report about the contested referendum.

Earlier on Monday, White House spokesman Sean Spicer said the U.S. administration would wait until a report by international observers mission.