Democratic presidential nominees Hillary Clinton and Bernie Sanders sought to attack each other's credibility in Thursday night's debate in Brooklyn.

Sanders said Clinton had shown poor judgment by accepting money from Wall Street for speeches and supporting free trade deals. He also attacked her decision to back the US invasion of Iraq in 2003. But the Vermont senator stopped short of repeating previous statements questioning the former secretary of state's qualifications to be president.

"Does Secretary Clinton have the intelligence, the experience to be president? Of course she does, but I do question her judgment," Sanders said. "I question her judgment which voted for the war in Iraq, the worst foreign policy blunder in the history of this country."

Clinton, 68, hit back, accusing Sanders of failing to explain how he planned to achieve his signature policy proposals, including breaking up big banks.

"You need to have the judgment on day one to be both president and commander-in-chief," Clinton said.

Exchange of fire

The string of aggressive jabs prompted CNN moderator Wolf Blitzer to warn, "If you're both screaming at each other, the viewers won't be able to hear either of you."

During the debate, Clinton pledged to sign a bill raising the minimum wage nationally to $15 (about 13 euros). Sanders, meanwhile, criticized her for refusing to release the transcripts of her paid speeches given to Wall Street banks.

Clinton in turn raised questions about his transparency and asked why he had not released his tax returns. Sanders replied by saying he would release his full 2014 returns on Friday and said there would be "no big money from speeches, no major investments" in the disclosures.

Clinton also challenged Sanders over his vote in Congress for a bill protecting gun manufacturers from being sued over the criminal use of their products.

Key primary

The ninth Democratic debate came five days ahead of a high-stakes primary in New York. The last several opinion polls taken in the state have given Clinton, who served as the state's senator for two terms, a double-digit lead over Brooklyn-born Sanders.

Sanders, 74, has won the last eight state Democratic nominating contests, but he has so far failed to make a dent in Clinton's commanding lead in the race for the 2,383 delegates needed to clinch the party's presidential nomination.

The two candidates are vying for the 247 Democratic delegates up for grabs in the New York primary. Clinton has accumulated 1,289 pledged delegates from primaries and caucuses, while Sanders has 1,038. Her lead expands considerably when factoring in support from super-delegates - the party insiders who can back the candidate of their choice.

Protesters target Trump

On the Republican side, frontrunner Donald Trump addressed a state party gala at the Grand Hyatt hotel in New York, urging voters to give him a victory in the state's primary next week.

Outside the venue, angry protesters hung an effigy of the mogul and chanted "How do you spell racist? T-R-U-M-P." Police arrested 11 protesters who had tried to storm the hotel before the event got underway.

Trump's rivals, Texas Senator Ted Cruz and Ohio Governor John Kasich, have been chipping away at his lead, meaning he could be forced to fight for the nomination at a contested convention in Cleveland when Republicans gather to choose their nominee in July.

nm/sms (Reuters, AP, AFP)