Donald Trump repeatedly struggled to say the word “origin” during a White House meeting with the Nato secretary general in which the US president made a number of false claims.

Taking questions from reporters while sat alongside Jens Stoltenberg in the Oval Office, Mr Trump railed against Democrats in congress providing oversight of him and called for an investigation into why the special counsel’s probe into Trump campaign ties with Russia was launched.

“I hope they now go and take a look at the oranges, the oranges of the investigation, the beginnings of that investigation,” Mr Trump said. “You look at the origin of the investigation, where it started, how it started, who started it, whether it’s McCabe or Comey or a lot of them.

“Where does it go, how high up in the White House did it go? You will all get Pulitzer Prizes, OK? You’ll all get Pulitzer Prizes. You should have looked at it a long time ago and that’s the only thing that’s disappointing to me about the Mueller report.

“The Mueller report I wished covered the oranges, how it started, the beginnings of the investigation, how it started. It didn’t cover that, and for some reason none of that was discussed.”

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Special counsel Robert Mueller’s report, which has yet to be made public, cleared the president of conspiracy of Russia, but did not rule on whether he obstructed justice. Mr Trump wrongly claimed it cleared him of both.

The president has repeatedly claimed he was the subject of an illegal “witch hunt” invented by senior government officials and even former president Barack Obama. He has never provided evidence to back his claims.

In a freewheeling press conference, Mr Trump also railed against immigration across the southern border, said he had “to get rid of judges” who deal with asylum cases, and falsely claimed only two per cent of immigrants detained by border agents under so-called “catch and release” attend court for their application hearing.

The true figure is at least 60 per cent, according to Justice Department figures.

Mr Trump also threatened to close “large sections” of the border – admitting it would impact trade but that security was “more important” – and said, without providing evidence, that Central American countries “arrange these caravans” the president has repeatedly cited as evidence of an emergency situation at the border.

Asked about Germany’s contributions to Nato, Mr Trump accused Berlin of “not paying their fair share” before wrongly claiming his father was born in Germany.

“My father is German, right? Was German, and born in a very wonderful place in Germany, so I have a great feeling for Germany,” he said. His father was in fact born in the US.

Later on Tuesday evening, at a National Republican Congressional Committee event, Mr Trump ventured into new territory when he untruthfully claimed wind turbines cause cancer.

Donald Trump incorrectly says that his father was born in Germany: 'My father is German, was German. Born in a very wonderful place in Germany'

“If you have a windmill anywhere near your house, congratulations, your house just went down 75 per cent in value,” Mr Trump told his audience. “And they say the noise causes cancer. You tell me that one, OK? Rerrrr rerrrr!”

There is no evidence the noise from windmills or turbines causes cancer.

He also revealed he had called authoritarian Chinese president Xi Jinping a “king” during a visit to Beijing in 2017.