A fourth former FTX executive has pleaded guilty in the US in a case stemming from the dramatic collapse and bankruptcy of the once popular cryptocurrency exchange.

Ryan Salame, one of the firm's top executives, admitted he had violated campaign finance laws and operated an illegal money-transmitting business.

He agreed to surrender more than $1.5bn (£1.2bn) to authorities.

The pleading comes ahead of the October trial of FTX founder Sam Bankman-Fried.

Mr Bankman-Fried, the so-called former 'King of Crypto, was arrested last year on fraud charges, after FTX filed for bankruptcy, leaving many users unable to withdraw their funds.

Prosecutors have said the fall stemmed from a massive scheme run by Mr Bankman-Fried. He is accused of misusing money from investors and customers from FTX to pay for property, political donations and plug losses at his hedge fund, Alameda Research.

He has denied the allegations and was recently returned to jail to await trial.

Mr Salame started working at Alameda in 2019 and became co-chief of FTX's Bahamas unit and a major political donor.

He is the fourth top executive from Mr Bankman-Fried's companies to plead guilty to charges, after former Alameda chief executive officer Caroline Ellison, former FTX technology chief Gary Wang and former FTX engineering chief Nishad Singh.

Mr Salame on Thursday admitted to using money from Alameda and using false names to illegally make millions of dollars of donations, exceeding legal limits.

Prosecutors also said he was involved in using Alameda accounts to process FTX customer funds, misrepresenting the activity to the bank involved, which had asked for more due diligence and proper registration when asked to work directly with FTX.

"Ryan Salame agreed to advance the interests of FTX, Alameda Research, and his co-conspirators through an unlawful political influence campaign and through an unlicensed money transmitting business, which helped FTX grow faster and larger by operating outside of the law," said prosecutor Damian Williams, US attorney for the southern district of New York.

Though Mr Salame has agreed to surrender $1.5bn, authorities said they would accept $6m, two properties in Massachusetts and a 2021 Porsche as part of the plea deal, according to Reuters.