WASHINGTON (AFP) - Top US diplomat Rex Tillerson does not plan to step down, the State Department said on Tuesday (July 25), quashing reports citing differences with the White House.

Since taking the helm of the State Department in February, the former ExxonMobil chair has come under fire for his ultra-low profile, and his plan to slash by 30 per cent the budget of an agency that employs more than 70,000 people in Washington and around the world.

CNN reported that Mr Tillerson planned to leave by year's end, which spokesman Heather Nauert flatly denied.

"That is false. We have spoken with the secretary. The secretary has been very clear he intends to stay here at the State Department," she told reporters.

"We have a lot of work that is left to be done ahead of us. He recognises that. He's deeply engaged in that work."

Pressed about Mr Tillerson's light schedule in recent days, Ms Nauert said the secretary was "just taking a little time off".

"He's had a lot of work. He just came back from that mega trip overseas, as you all well know," the spokesman added, referring to a trip that took Mr Tillerson to the G20 summit in Germany as well as to Turkey, Ukraine and Gulf countries. "So, he's entitled to take a few days himself."

Many US ambassadorial and management posts have not been filled, with diplomats and experts fretting they could be next on the budget chopping block.

CNN said that among Mr Tillerson's growing differences with the White House were fresh debates over Iran policy and personnel, as well as US President Donald Trump's chaotic and confusing foreign policy approach.