In a telephone call, Trump called on Erdogan to "de-escalate" the attack on Afrin and expressed concern about "the destructive and false" anti-American rhetoric emanating from Turkey.
Over the weekend Turkish forces backed by local Syrian Arab fighters launched an incursion into Afrin, a border canton administered by a local Kurdish-led council and defended by the YPG militia.
United States forces work with and support the YPG in the east of Syria, where Kurdish fighters form the backbone of the local force that drove the Islamic State group out of its "capital" Raqa.
But Turkey sees the entire YPG group as a "terrorist" faction of the banned PKK Kurdish guerrilla government which has been fighting a deadly insurgency inside Turkey for three decades.
Kurdish leaders have demanded that the United States rein in Turkey, a NATO ally, and vowed to resist its cross-border operation.
According to a White House statement, Trump "urged Turkey to de-escalate, limit its military actions, and avoid civilian casualties and increases to displaced persons and refugees.
"He urged Turkey to exercise caution and to avoid any actions that might risk conflict between Turkish and American forces," it added.
The US has more than 2,000 special forces and support troops inside Syria, mainly east of the Euphrates in an area also controlled by the YPG but separate from Afrin, which is west of the river.
