"This war. What we're doing is got to stop at some point, ' Trump told CBS" "Face the Nation" on Sunday.
Full quote: "We spent a fortune on building this incredible base", Trump told Face the Nation. "We might as well keep it".
"I want to be able to watch Iran", he added, but denied he had plans to strike Iraq's neighbour.
This is not the first time the Iraqi government has expressed an unwillingness to host an estimated 5,200 American troops.
Opponents included every senator considering a 2020 presidential run, and four Republicans, who said USA foreign policy needs a rethink.
Trump's comments added to concerns in Iraq about America's long-term intentions, particularly after it withdraws its troops from Syria.
Warnings of travel disruption after temperatures fall to -15C overnight
But it is far from the lowest United Kingdom temperature recorded there in January 1982, when it reached -27.7C (-17.86F). The freezing temperatures have led to weather warnings being issued by the Met Office for snow, ice and fog into Friday.
"Members of parliament's security, defence and foreign relations committees are now working hard to determine the exact number and real mission of the USA forces in Iraq", a high-level Iraqi government source told The New Arab's Arabic edition.
American troops have been based in Iraq since the 2003 US-led invasion, which toppled dictator Saddam Hussein.
President Trump announced in December that he would be pulling troops out of Syria, saying ISIS "has been defeated".
In response, Pentagon officials said the group was "well-positioned to rebuild and work on enabling its physical caliphate to re-emerge".
However, he said "Now, that doesn't mean we're not going to be watching with intelligence".
On Sunday, former Iraqi Prime Minister Haider al Abadi also criticized remarks by Trump, the Iraqi News reported.
Abadi further called on the government to affirm Iraq's unshakable stance that "Iraqi territory can not be used against any neighboring country or any party".
There are an 5,000 estimated United States military personnel in Iraq authorised to train, advise and assist Iraqi security forces in their fight against IS, which has not fully controlled any territory in the country for more than a year.
The BBC's Paul Adams says this poses a problem for the government in Baghdad and could complicate delicate negotiations over USA use of the Al Asad Airbase. Iraqi military personnel discovered and managed to defuse three Grad rockets pointed at the base set with electronic timers. It also said that ISIS is likely to regain territory after the US leaves.