US troops have crossed into Iraq from Syria through the Sahela border crossing in the northern province of Dohuk, Reuters witnesses said on Monday. Reuters video images showed armored vehicles carrying troops into Iraq, part of the US withdrawal from Syria. A Reuters cameraman saw more than 100 vehicles crossing. An Iraqi Kurdish security source also told the news agency that US troops had crossed into the semi-autonomous Kurdistan Region of Iraq. About 30 trailers and Hummers carrying heavier duty equipment crossed, with troops in cars coming through, the source added. A second security source in Mosul also said US troops had crossed into Iraq from Sahela. US Defense Secretary Mark Esper said on Saturday that all of the nearly 1,000 troops withdrawing from northern Syria are expected to move to western Iraq to continue the campaign against ISIS militants and "to help defend Iraq". Esper did not rule out the idea that US forces would conduct counterterrorism missions from Iraq into Syria. But he told reporters traveling with him that those details will be worked out over time. Acting chief of staff Mick Mulvaney told "Fox News Sunday" that "the quickest way to get them out of danger was to get them into Iraq." On Thursday, Turkey agreed in talks with US Vice President Mike Pence to a five-day pause in an offensive into northeastern Syria to allow time for the Kurdish fighters to withdraw from a "safe zone" Ankara aims to establish near its border with Syria. The truce also aimed to ease a crisis triggered by President Donald Trumps abrupt decision this month to withdraw all 1,000 US troops from northern Syria, a move criticized in Washington and elsewhere as a betrayal of loyal Kurdish allies who had fought for years alongside US troops against ISIS. Between 200 and 300 US troops will remain at the southern Syrian outpost of al-Tanf.