Smoke billows from a fire inside Syrian territory during a bombardment by Turkish forces on Wednesday. Photo: AP

Beirut – President Donald Trump says the US does not endorse Turkey's assault on northern Syria and has made it clear to Ankara that its incursion against Kurdish fighters who helped the US battle the Islamic State is a "bad idea".

In a statement on Wednesday, Trump said no American soldiers are in the area being invaded. Earlier, Trump ordered US forces out of the area, prompting criticism that he was abandoning an American ally.

Trump says he does not want the US to fight "these endless, senseless wars".

He says he will hold Turkey to its commitment to protect civilians and religious minorities, including Christians, and ensure the invasion does not create a humanitarian crisis. He also says Turkey must make sure that IS fighters held captive in Syria remain detained.

Earlier, a US defence and a Kurdish official in Syria said the American-backed Syrian militia being attacked by Turkish forces has suspended operations against the Islamic State group.

The militia, known as the Syrian Democratic Forces, has been moving into position to contest the Turkish onslaught, which so far includes airstrikes and artillery barrages.

The officials who confirmed the SDF suspension of operations against the Islamic State, were not authorised to provide details on the unfolding situation and so spoke on condition of anonymity.

The US defence official said an incursion by Turkish ground forces had not yet begun but was expected soon.

Egypt has condemned Turkey's military operation into northern Syria, calling it an "aggression" against Syria's sovereignty.

Egypt's Foreign Ministry  condemned "in the strongest words" the offensive and called for the UN Security Council to halt "any attempts to occupy Syrian territories or change the demographics in northern Syria".

The statement said Turkey's attack is a "blatant aggression" against Syria's sovereignty. It also calls for an emergency meeting of the Arab League.

A Syrian war monitor and a Kurdish activist collective said Turkish bombardment of northern Syria has killed at least one member of the Kurdish-led force.

The Britain-based Syrian observatory for Human Rights said one fighter of the US-backed Kurdish-led Syrian Democratic Forces was killed and six others were wounded.