Turkey has legitimate security concerns in northeast Syria, US Secretary of State Mike Pompeo said, as the 120-hour lull in the fighting in the region is set to expire. It is unclear if the temporary cease-fire will be replaced by the permanent one, which Pompeo and US Vice President Mike Pence spoke about in Ankara last week, when they set in place a 120 hour window to allow Kurdish YPG fighters to withdraw from the proposed "safe zone."The five-day truce in Turkey's cross-border operation ends at 10 pm (1900 GMT) on Tuesday. Turkish-backed Syrian rebels are ready to resume their offensive if Kurdish YPG militants don't withdraw from the border area before the U.S. brokered truce ends, a field commander said on Tuesday.“We are mindful that our NATO ally, Turkey has legitimate security concerns there [in northeast Syria.] Indeed the US has designated the PKK as terrorists for an awfully long time,” Pompeo said, as he spoke at the Heritage Foundation’s Annual President’s Club Meeting in Washington, D.C.“We take those concerns seriously. So we were working, the state department in the lead along with our brethren at the Department of Defense, to build out a safe zone within the region. “Trump warned Turkey not to invade, sadly they conducted the incursion,” Pompeo said.“In just a few hours the 120 hour window will arrive.. some progress has certainly been made,” he said. "The truth is that it was in Turkey’s interest as a NATO ally to continue with that incursion."Trump used economic might, “our economic power to avoid a kinetic conflict with a NATO ally,” and as the President said, he used “tough love” to get it done, Pompeo said. "The success of the outcome in northeast Syria, has yet to be determined,” he added.Pompeo blamed the situation on the former administration. The Trump administration inherited a “mess” in Syria, Pompeo said, adding that the explained that the Obama administration had allowed the Islamic Caliphate to take root in Syria and Western Iraq.It was the Trump administration that built a coalition, with 70 nations and the help of the SDS fighters, that built a coalition to combat ISIS, Pompeo said. “The Kurdish forces there, the Arab fighters, that were part of the SDF were great warriors,” Pompeo said. On Tuesday, hundreds of Kurdish fighters remained near to Syria's northeast border despite a U.S.-brokered truce demanding their withdrawal. Turkey could resume its offensive in the area when the ceasefire expires, Turkish President Tayyip Erdogan said. "The withdrawal is continuing," Erdogan told reporters at Ankara airport before flying to Russia for talks on Syria with President Vladimir Putin, who supports the Damascus government and has also sent troops to northeast Syria."We are talking about 700-800 (YPG fighters) already withdrawn and the rest, around 1,200-1,300, are continuing to withdraw. It has been said that they will withdraw," Erdogan said. "All will have to get out, the process will not end before they are out."Trump said on Monday it appeared that the five-day pause was holding despite skirmishes, and that it could possibly go beyond Tuesday's expiry, but Erdogan said the fighting may resume.Reuters contributed to this report.