Tensions in the Middle East spiraled last week after Trump called for a U.S. airstrike in Baghdad that killed a top Iranian general, Qasem Soleimani.
Speaking to reporters on Air Force One, the U.S. president said: "If they do ask us to leave, if we don't do it in a very friendly basis, we will charge them sanctions like they've never seen before ever. It'll make Iranian sanctions look somewhat tame."
"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 said.
The president added that "If there's any hostility, that they do anything we think is inappropriate, we are going to put sanctions on Iraq, very big sanctions on Iraq."
Soleimani, the head of a special forces unit in the Islamic Revolutionary Guard Corps, was the key architect of Iran's military operations overseas.
He was killed late Thursday while leaving Baghdad airport, when his convoy was struck by a drone, ordered by the U.S. president. One of those killed with him was a key Iraqi militia leader, Abu Mahdi al-Muhandis, who was the deputy commander of Iran-backed militias known as the Popular Mobilization Forces.
The Iraqi government has accused Washington of violating its sovereignty.
"The Iraqi government must work to end the presence of any foreign troops on Iraqi soil and prohibit them from using its land, airspace or water for any reason," read the resolution passed by the Iraqi parliament, which convened in an extraordinary session on Sunday.
The U.S. ambassador to Iraq is set to meet a Iraqi Prime Minister Adel Abdul Mahdi on Monday to talk about the future of American military troops in Iraq, two U.S. officials familiar with the matter told NBC News. They said the U.S. was expecting Mahdi to inform the ambassador of its decision to expel U.S. troops in Iraq.
Soleimani's death marked a dramatic escalation in tensions between the U.S. and Iran, which was already deteriorating after Trump in 2018 unilaterally withdrew from the landmark Iran nuclear deal brokered by the Obama administration.
Tehran has vowed revenge for the commander's targeted killing.
Asked by reporters on Air Force One if he was worried about retaliation from Iran, Trump said: "If it happens it happens. If they do anything there will be major retaliation."
"They're allowed to kill our people. They're allowed to torture and maim our people, they're allowed to use roadside bombs and blow up our people. And we're not allowed to touch their cultural sites. It doesn't work that way."
On Saturday, Trump said in a series of tweets that the U.S. has targeted 52 sites "at a very high level and important to Iran and Iranian culture."
Trump warned in those tweets that the U.S. will strike those targets "very fast and very hard" if Iran retaliates.