ABOARD AIR FORCE ONE - US President Donald Trump threatened sanctions against Baghdad on Sunday after Iraq 's parliament called on US troops to leave the country, and the president said if troops did leave, Baghdad would have to pay Washington for the cost of the air base there.“We have a very extraordinarily expensive air base that’s there. It cost billions of dollars to build, long before my time. We’re not leaving unless they pay us back for it," Trump told reporters on Air Force One.Trump said that if Iraq asked US forces to leave and it was not done on a friendly basis, "we will charge them sanctions like they’ve never seen before ever. It’ll make Iranian sanctions look somewhat tame.”Before Trump's comments to reporters, a State Department spokeswoman said the United States was waiting for clarification of the legal nature and impact of the resolution, and strongly urged Iraqi leaders to reconsider the importance of the two nations' ongoing economic and security relationship.Some 5,000 U.S. troops remain in Iraq, most in an advisory role.Abdul Mahdi said that despite the "internal and external difficulties" the country might face, canceling its request for help from U.S.-led coalition military forces "remains best for Iraq on principle and practically."He said he had been scheduled to meet Soleimani the day he was killed , and that the general had been due to deliver an Iranian response to a message from Saudi Arabia that Abdul Mahdi had earlier passed to Tehran. Sunni Muslim Saudi Arabia and Shi'ite Iran had been about to "reach a breakthrough over the situation in Iraq and the region," Abdul Mahdi said.Despite decades of U.S.-Iran enmity, Iranian-backed militia and U.S. troops fought side by side during Iraq's 2014-17 war against Islamic State, their common enemy. Iraqi militia leader Abu Mahdi al-Muhandis was also killed in Friday's strike.Sunday's parliamentary resolution was passed by overwhelmingly Shi'ite lawmakers, as the special session was boycotted by most Sunni Muslim and Kurdish lawmakers.One Sunni member of parliament told Reuters both groups feared that kicking out U.S.-led forces would leave Iraq vulnerable to insurgents, undermine security and heighten the power of Iranian-backed Shi'ite militias.During the evening Trump also spoke with UK Prime Minister Boris Johnson, discussing the current situation in Iraq and Iran, the White House said in a statement.The release offered few details of the specifics of the call, noting only that the two leaders "reaffirmed the close alliance between the two countries."