President Donald Trump took aim at the US Federal Reserve twice on Friday, knocking the system in person and on Twitter for interest rates he said are too high.

In a tweet late Friday, Trump wrote that the most "difficult problem" facing the US economy "is not our competitors, it is the Federal Reserve!"

The president was doubling down on comments he made earlier that day, in which he insisted that if interest rates were cut, the US "would be like a rocket ship."

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President Donald Trump took aim at the US Federal Reserve on Twitter late Friday, hours after knocking the banking system.

Trump seemed to be partially referring to a report from the Labor Department that said the US economy added 224,000 jobs in June, which Trump argued should encourage the federal body to cut interest rates.

"Strong jobs report, low inflation, and other countries around the world doing anything possible to take advantage of the United States, knowing that our Federal Reserve doesn't have a clue!" Trump wrote. "They raised rates too soon, too often, & tightened, while others did just the opposite."

Trump continued, pointing to the state of the country "the day after the great Election, when the Market shot right up," saying "it could have been even better - massive additional wealth would have been created, & used very well."

He added: "Our most difficult problem is not our competitors, it is the Federal Reserve!"

The tweet was a double-down from Trump on comments he made earlier that day at the White House.

"We don't have a Fed that knows what they're doing, so it's one of those little things," Trump told reporters at the White House on Friday. If interest rates were cut, Trump insisted, the US "would be like a rocket ship."

Read more: Trump attacks Fed again, saying they don't know what they're doing and calling for rate cuts

This is Trump's latest call for lower interest rates by the Fed. He previously has pointed to former President Barack Obama's administration as the ideal landscape of interest rates.

"He paid close to zero interest rates," Trump said of Obama again Friday. "I'm paying real interest."

Carmen Reinicke contributed reporting.