"I'm not thrilled with his raising of interest rates, no. I'm not thrilled," Trump said in the interview.
The president also said China is manipulating its currency and the Europeans are manipulating the euro, Reuters reported Monday. And he told the news outlet that he wasn't concerned about the potential for economic damage to Europe after the U.S. imposed tariffs on Turkey, saying "there will be no concessions" with Turkey.
Trump nominated Powell to succeed former Fed Chair Janet Yellen earlier this year. The central bank has raised rates five times since Trump took office, twice since Powell became Fed chairman.
Monday's comments come just weeks before the Fed meets again to consider rates. It is widely expected to raise them in September and possibly later this year.
It is unusual for presidents to openly criticize Fed chairs, who are supposed to be independent. But Trump already did so in an interview on CNBC earlier this summer. "These types of comments could be perceived to threaten the autonomy of the Federal Reserve," said Lindsey Piegza, chief economist at Stifel.
With a strong job market and economic growth humming along, the Fed has been working to push rates back up from historic lows a decade after it flooded the financial system with money to help it recover from the financial crisis. The Fed has long telegraphed its intention to raise rates back to a neutral level.
"This is by any measure this is a very solid U.S. economy, supported by fiscal policy, private solid spending," said Nathan Sheets, chief economist at PGIM Fixed Income. "By any theory of central banking, they need to move the rate back to neutral. There are many more risks if they fail to do that. There's a strong case for the Fed to act pre-emptively."
The comments on currency manipulation are also potentially sensitive, as officials from China meet with U.S. officials this week on restarting trade talks after a round of tariffs escalated tensions between the two countries. Trump told Reuters that he had "no time frame" for ending the trade dispute with China and that he does not anticipate much coming out of this week's talks.
CNBC's Thomas Franck
Read the Reuters story here.