President Donald Trump called Turkish president Recep Tayyip Erdogan on Monday to congratulate him after Erdogan narrowly emerged victorious from a referendum to inflate his political powers, Turkish officials said and the White House confirmed.

Preliminary results showed 51.4 percent of voters had voted “yes.” The changes could keep Erdogan in power for more than 10 more years, and allow him to select and remove members of his cabinet unilaterally.

The referendum process occurred on an “unlevel playing field,” according to international observers in Turkey who monitored the lead-up to the vote. Not only did some “no” voters face intimidation at the polls, the observers said Monday, but the ballots themselves didn’t even state what the vote was about.

In a statement Monday evening, the White House said Trump spoke to Erdogan “to congratulate him on his recent referendum victory and to discuss the United States’ action in response to the Syrian regime’s use of chemical weapons on April 4th.”

“President Trump thanked President Erdogan for supporting this action by the United States, and the leaders agreed on the importance of holding Syrian President Bashar al-Assad accountable,” the statement added. “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.”

German chancellor Angela Merkel had a slightly different reaction to the news of the change in Erdogan’s powers. “The tight referendum result shows how deeply divided Turkish society is and that means a big responsibility for the Turkish leadership and for President Erdogan personally,” she said.

Other countries to offer their congratulations to Erdogan included Qatar, Azerbeijan, Saudi Arabia and Sudan, Turkish state media said.

This story has been updated to include comment from the White House.