Trump called the Turkish leader on Monday shortly after international monitors delivered a harsh verdict on the referendum on constitutional changes. They found that the opposition campaign had been restricted and the media coverage was imbalanced, and that the electoral authority had unfairly changed the rules after polls had opened.
Trump joins a short list of leaders who have openly congratulated Erdogan, including Azerbaijani President Ilham Aliyev and Saudi King Salman.
His congratulations stands in stark contrast to the more cautious tone adopted by European leaders and a statement issued by the US State Department, which acknowledged the results but warned against further repression by the Turkish government of the political opposition.
"We look to the government of Turkey to protect the fundamental rights and freedoms of all its citizens -- regardless of their vote on April 16 -- as guaranteed by the Turkish constitution and in accordance with Turkey's international commitments," the State Department said in a statement.
"Democracies gain strength through respect for diverse points of view, especially on difficult issues."
The Turkish government has been widely condemned by Western nations for its repression of opposition figures following a failed military coup last year.