A key witness in former special counsel Robert Mueller’s Russia probe was busted Monday on a child pornography charge at JFK Airport — and got locked up overnight after a prosecutor said he was suspected of even worse sex crimes.

George Nader, 60, was accused of possessing a dozen videos featuring boys as young as 3 — with some also involving goats and chickens — on an iPhone that was seized from him last year.

A criminal complaint charging Nader with transporting material involving the sexual exploitation of minors was later filed under seal in Virginia.

It was unsealed following his arrest at JFK, where court papers say he arrived on a flight from Dubai.

The case marks the latest in a series of accusations against the Lebanese-American businessman that involve child pornography or sex with minors and stretch back to 1985.

Nader — who serves as an adviser to Mohammed bin Zayed Al Nahyan, crown prince of the United Arab Emirates — is mentioned more than 100 times in the redacted version of Mueller’s report that was made public in April.

It details efforts by Kirill Dmitriev, a Russian banker with ties to Russian President Vladimir Putin, to have Nader introduce him to members of President Trump’s campaign.

The report also describes Nader’s role in arranging a January 2017 meeting in the Seychelles between Dmitriev and Erik Prince — founder of the Blackwater security company and brother of Education Secretary Betsy DeVos — following Trump’s election.

Monday’s child pornography charge stems from the seizure of three iPhones from Nader when he passed through a customs checkpoint at Washington-Dulles International Aiport in Dulles, Virginia, on Jan. 17, 2018.

Court papers say the search warrant for Nader’s phones was “for a matter not involving child pornography,” and his lawyer said in Brooklyn federal court Monday that the phones were handed over to Mueller’s office.

Magistrate Judge Cheryl Pollak ordered Nader jailed pending a bail hearing Tuesday after a prosecutor said Nader was suspected of having “transported underage children for the purpose of having sex.”

Assistant US Attorney Miriam Glaser Dauerman also alleged that Nader “has every incentive to flee and every ability to flee,” saying, “He works for and has connections at the highest levels in the United Arab Emirates and Saudi Arabia.”

Dauerman noted that the US has no extradition treaty with the UAE.

Defense lawyer Christopher Clark said Nader — who wore a wrinkled shirt and khakis with no belt — came to New York for treatment of a heart ailment, calling him a “sick man” who “needs to be in a medical facility.”

Clark also said Nader was willing to “post every penny” of his $3 million net worth to secure his freedom.

Nader was arrested in 1985 for allegedly importing child pornography into the US from the Netherlands but beat the rap on a technicality.

He pleaded guilty to possessing child pornography in 1991 but got a reduced sentence of just six months in jail and had the case file sealed for helping to free American hostages who were being held in Lebanon, according to the Washington Post.

He also convicted of sexually abusing minors in the Czech Republic and sentenced to one year in jail in 2003.

With Post wires