US President Donald Trump called his Turkish counterpart Recep Tayyip Erdogan on Monday to congratulate him on winning the referendum boosting his powers, Turkish state media reported.

"Trump called Erdogan tonight (Monday) and congratulated him on his success in the referendum," Turkish presidential sources said, quoted by state-run news agency Anadolu after Erdogan won over 51 percent in Sunday's vote.

The reaction from Trump contrasts with EU leaders who have been reserved in their reaction to the narrow victory while monitors expressed concern over the "unlevel playing field".