Executives of eight major cryptocurrency firms have been called to testify before a US congressional committee on 8 December.

Witnesses called to appear include Coinbase's Alesia Haas, Circle's Jeremy Allaire and Bitfury's Brian Brooks.

It will be the first time companies representing the controversial sector have been questioned in this way.

US politicians across the political spectrum have called for more scrutiny of crypto-currencies.

Elizabeth Warren on the left of the Democratic Party has called for tougher regulation of the sector and Donald Trump has described crypto-currencies as "a scam".

Mr Brooks of Bitfury previously served as a top banking regulator under the Trump administration and had a role in policy-making around crypto-currencies.

Indian government set to ban crypto-currencies
El Salvador plans Bitcoin city at base of volcano
New York's next mayor wants to be paid in Bitcoin
Crypto-currencies are not currencies in the traditional sense, although they can sometimes be used to make payments. They are stored online in a "digital wallet" and act more like investment vehicles or securities, often with a high degree of volatility.

The anonymity of paying using crypto-currencies means they have been favoured for criminal activities such as drug dealing and ransomware attacks. However their supporters say the view that they are predominantly for circumventing the law is outdated and that innovation in this area offers huge potential.

Countries around the world have taken radically different approaches to crypto-currencies.

China has declared crypto-currency transactions illegal, a move India looks set to follow. Many other central banks are eyeing the sector warily and discussing regulation.

However El Salvador recently declared Bitcoin - the most widely established crypto-currency - to be legal tender and its president plans to build a Bitcoin city at the base of a volcano, with the cryptocurrency used to fund the project.

Across the US, as well as many private citizens holding crypto-currencies, states and municipalities have begun toying with plans to integrate them into their operations.

The mayor of Miami and mayor elect of New York have ambitions to make their cities centres for cryptocurrency business.

The hearing before the US House Financial Services Committee will focus on "the challenges and benefits of financial innovation", according to the committee announcement.

The other chief executives who have been asked to appear are Sam Bankman-Fried of FTX Trading, Chad Cascarilla of Paxos and Dennelle Dixon of the Stellar Development Foundation.