US President Donald Trump is expected to express American unease over a Turkish cross-border offensive into Syria, in a call scheduled with counterpart Recep Tayyip Erdogan, US officials said Tuesday.

"They are likely to talk soon," said a senior US administration official, confirming reports of a Trump-Erdogan call set for Wednesday.

The US is urging restraint from Ankara after the Turkish military hit Kurdish militias that had aided the American-led fight against Daesh.

The US government and the National Security Council are "concerned about the situation", said a second senior administration official.

"We hear and we take very seriously Turkey’s legitimate security concerns," but, he added that "It detracts from efforts to fight [Daesh]".

"We are urging Turkey to exercise restraint in its military actions and rhetoric (and) to ensure that its operations are limited in scope and duration," the second official added.