image copyrightGetty Imagesimage captionMr Barrack (centre) was a long-time friend of Donald Trump

Billionaire investor and former Donald Trump adviser Thomas Barrack has pleaded not guilty to charges of acting as an agent of a foreign government.

Mr Barrack, 74, was a key aide to Mr Trump during his 2016 campaign.

He has been accused of illegally lobbying on behalf of the United Arab Emirates (UAE) during and after the election, as well as lying to the FBI.

Mr Barrack entered his not guilty plea during his first court appearance on Monday in New York City.

The ex-Trump official faces federal charges of conspiracy, obstruction of justice and making multiple false statements to the FBI during a 2019 interview. He was arrested in California last week.

As he left court on Monday, Mr Barrack told reporters: "As you'd expect, the system is working… you'll all see that I'm 100% innocent."

Mr Barrack's employee, Matthew Grimes, also faces illegal lobbying charges and pleaded not guilty on Monday. A UAE citizen, Rashid Sultan Rashid Al Malik Alshahhi, 43, was also charged and remains at large.

The three men are accused of unlawfully trying to promote UAE government interests by using Mr Barrack's connections to influence officials and media appearances.

They also allegedly promoted the candidacy of a UAE-favoured individual as US ambassador to Abu Dhabi.

Mr Barrack, who also served as Mr Trump's inaugural committee chairman, had been friends with the former president for four decades.

The wealthy investor is the latest ex-Trump aide to face criminal charges, like former campaign chairman Paul Manafort and former Trump Organization lawyer Michael Cohen.

His next court appearance is 2 September.

Mr Barrack is currently free on a $250m (£180m) bond, but must wear an electronic GPS ankle bracelet, restrict his travel and follow a curfew.