President Donald Trump said he was unsure whether his top diplomat, Rex Tillerson, would remain in his post for the rest of Trump's term in the White House and was "not happy" that some State Department staff were not supporting his agenda.

In an interview with Laura Ingraham on Fox News late Thursday, Trump attacked the department under Secretary of State Tillerson and said he alone determines U.S. foreign policy.

"The one that matters is me," Trump said. "I'm the only one that matters because, when it comes to it, that's what the policy is going to be."

Asked if he planned to keep Tillerson on board for the rest of his term, Trump told Fox, "Well, we’ll see. I don’t know."

Trump left on Friday on a trip to Asia with Tillerson following months of conflict between the two.

Trump's comments drew criticism in Congress, where many fellow Republicans have joined Democrats in objecting to Trump's plan to slash spending on diplomacy and foreign aid, and his failure to fill key foreign policy jobs.

"One would hope that if he's the only one that matters that he at least gets some feedback from top staff who perhaps can know a little bit more about some of these things than he does," Representative Eliot Engel, top Democrat on the House of Representatives Foreign Affairs Committee, told Reuters.

Tensions between Trump, a real estate developer and reality television star in office since January, and Tillerson, former chief executive at Exxon Mobil Corp, resurfaced last month amid reports Tillerson had called Trump a "moron" and considered resigning.

Tillerson later said he never considered leaving. Trump said they had a good relationship but criticized Tillerson as weak.

Tillerson's State Department has also been at odds with the White House over global issues including rising tensions over North Korea's nuclear program.

Richard Haass, president of the Council of Foreign Relations, said Trump's comments spelled trouble not just for the current secretary but for overall foreign policy.

"It's not just about Rex Tillerson, it's about who comes after Rex Tillerson. If the president is not determined to make sure his secretary of state will succeed, the secretary of state can't succeed," Haass told CBS News.

Tillerson has made overhauling the department a top priority and tightened control by consolidating his authority. Critics have decried the reorganization and unfilled jobs at a time when international crises continue around the world.

At a recent meeting of former national security advisers, former Secretary of State Colin Powell told H.R. McMaster, Trump’s national security advisor, that the administration was gutting State. McMaster replied that there were people who did not support the president’s agenda, two people present told Reuters.

On Thursday, Trump said many of the posts were not needed and he is "not happy" with others already there.

"I want my vision, but my vision is my vision," he said. "Rex is in there working hard ... he’s doing the best he can."