President Donald Trump lashed out at Rex Tillerson on Thursday morning after his former secretary of state reportedly told a House committee that the president was ill-prepared for a 2017 meeting with Russian President Vladimir Putin.

"Rex Tillerson, a man who is 'dumb as a rock' and totally ill prepared and ill equipped to be Secretary of State, made up a story (he got fired) that I was out-prepared by Vladimir Putin at a meeting in Hamburg, Germany," Trump tweeted. "I don’t think Putin would agree. Look how the U.S. is doing!"

The tweet followed a Washington Post report that Tillerson told the House Foreign Affairs Committee that Putin out-prepared Trump for the meeting at the 2017 G-20 summit. Tillerson said Putin's higher level of preparation put Trump at a disadvantage during the meeting.

The U.S. had anticipated a shorter meeting between the two leaders, but it instead turned into a two-hour plus discussion of geopolitical issues, committee aides told the Post. Tillerson spoke before the committee for seven hours in a closed-door session on Tuesday.

"We spent a lot of time in the conversation talking about how Putin seized every opportunity to push what he wanted," a committee aide told the Post. "There was a discrepancy in preparation, and it created an unequal footing."

Tillerson spoke with a bipartisan group of lawmakers and staff at the request of the panel's chairman, Rep. Eliot Engel, D-N.Y., the newspaper reported. Unlike Trump's solo meeting with Putin in Helsinki last summer, advisers — including Tillerson — were present alongside him at the meeting with the Russian president in Germany.

Tillerson and Trump had sparred for months before the president fired him in March of last year. The former secretary of state nearly resigned in the summer of 2017 amid mounting policy disputes and clashes with the White House, NBC News reported, citing senior administration officials. As tensions came to a head, Tillerson called Trump a "moron" following a meeting at the Pentagon with Cabinet officials and members of Trump's national security team, three officials familiar with the incident said.

In December, Tillerson told CBS News that Trump was "undisciplined," didn't read much and tried to do things that would violate the law. In response, Trump said Tillerson "didn’t have the mental capacity needed" to be secretary of state.

"He was dumb as a rock and I couldn’t get rid of him fast enough," Trump tweeted. "He was lazy as hell."

In hiring Tillerson to run the State Department, Trump pointed to the former Exxon Mobil executive's "vast experience at dealing successfully with all types of foreign governments" and called him "a world class player and dealmaker."

"He will be a star," Trump tweeted after Tillerson was sworn in.