Donald Trump has congratulated
Turkish President Recep Tayyip Erdogan on his victory in Sunday's
referendum that gave him sweeping new powers.
Mr Erdogan rejected criticism from international monitors who said he had been favoured by an "unequal campaign". "Know your place," he told the observers.
The narrow victory was ruled valid by Turkey's electoral body, despite claims of irregularities by the opposition.
In a separate development, Turkey extended the state of emergency for three months. The measure, introduced after a failed coup last July, was set to expire in two days.
Turkey divisions exacerbated
The referendum in numbers
In a statement on Monday, the White House said President Trump discussed with his Turkish counterpart America's "action in response to the Syrian regime's use of chemical weapons" on 4 April.
It said the two leaders "agreed on the importance of holding Syrian President Bashar al-Assad accountable". They also discussed "the counter-ISIS [Islamic State campaign]", the statement added.
Relations between Washington and Ankara have recently been strained by several key issues. One of Turkey's main grievances with the US is the policy started by the Obama administration of supporting Kurdish fighters in Syria who are fighting IS forces.
Turkey views the Syrian Kurdish People's Protection Units (YPG) as a terror group linked to Kurdish separatists waging an insurgency inside Turkey since 1984.
The two sides are also at loggerheads over Fethullah Gulen. Turkey accuses the cleric of orchestrating the failed coup.
Officially the Washington insists any decision on returning him to Turkey from the US remains a judicial rather than a political one.