Hillary Clinton is continuing to resist calls to release her transcripts of paid speeches she gave to Goldman Sachs and other banks, saying she would hold onto them until Bernie Sanders and other rivals for the US presidency release theirs.

Sanders, her populist rival for the Democratic presidential nomination who has surged in polls with his furious rebukes of Wall Street and its role in the 2008 recession, said on Friday he had none to release because he does not give paid speeches to banks.

Clinton's reluctance to reveal what she privately told banks and other organisations has become an increasingly heated issue as she fights suggestions by Sanders and others that she is too cosy with the US financial industry.

"I am happy to release anything I have whenever everybody else does the same, because everybody in this race, including Senator Sanders, has given speeches to private groups," she said on Thursday night in a televised town hall event with voters in Nevada.

Nevada is the third state to vote for the Democratic Party's nominee in caucuses to be held on Saturday.

Clinton has earned more than $US20 million for 92 paid speeches since leaving her job as US secretary of state in 2013, according to records disclosed by her campaign, including $US675,000 for three closed-door speeches to New York-based investment bank Goldman Sachs.

She says this income has no influence on her policies and that she would increase Wall Street regulation.

Sanders, a US senator from Vermont, last gave a paid speech in 2004, according to his Senate financial disclosures, when he spoke about social activism at the California Institute of Technology in an event that was open to the public. He earned $US2000, according to his disclosures.

On Friday, Sanders' spokesman said the senator "accepts Clinton's challenge".

"He will release all of the transcripts of all of his Wall Street speeches," Michael Briggs said in a statement.

"That's easy. The fact is, there weren't any."

Briggs said he hoped this was sufficient for Clinton to release her transcripts.

Clinton's standard speaker's contract stipulated that the speech's host make a transcript that would then remain in Clinton's control.

Reuters