Hilary Clinton tore into Donald Trump at last night's Democratic presidential candidates debate saying he is fast becoming ISIS' best recuiting tool. 

The Democrat's front-running candidate attacked Trump, who leads the polls for the republican nomination, over his recent call for a "total and complete shutdown of Muslims entering the United States"

"He is becoming ISIS's best recruiter", she claimed.

"They are going to people showing videos of Donald Trump insulting Islam and Muslims in order to recruit more radical jihadists."

Instead Clinton said Americans need to work closely with Muslim communities because "they will be our early warning signal" against possible terrorist attacks.

"The first line of defense against radicalisation is in the Muslim American community -- people who we should be welcoming and working with," Clinton said.

The former secretary of state said she understood why thousands supported the millionaire property mogul but said he is inflaming people.

"A lot of people are understandably reacting out of fear and anxiety," she said. "Mr. Trump has a great capacity to use bluster and bigotry to inflame people and to make them think there are easy answers to very complex questions," she said.

Clinton also said that the country needed "to make sure the really discriminatory messages that Trump is sending around the world don't fall on receptive ears."

"I worry greatly that the rhetoric coming from the Republicans, particularly Donald Trump, is sending a message to Muslims here in the United States and literally around the world that there is a clash of civilizations, that there is some kind of Western plot or war against Islam, which then, I believe, fans the flames of radicalization," she added.

The debate was between the three contenders for the Democratic nomination: Hilary Clinton, Bernie Sanders and Martin O'Malley.

The three rivals were united in their condemnation of the republican nominees. However they attacked each other on gun control and on how best to combat ISIS.

Sanders said he did not want the US to be international policemen and said the troops on the ground fighting ISIS should be not American troops but should be Muslim troops.

When criticised that that method has been tried and failed and what would he do if it doesn't work, Sanders said "my plan is to make it work".

He attacked Clinton for focusing too much on regime change in Syria and said the US should focus solely on fighting ISIS.

However Clinton rejected his criticism and pointed out that Syrian rebels needed assurance Assad would be removed if they were to support the US' fight against ISIS.

"We will not get the support on the ground in Syria to dislodge ISIS if the fighters there who are not associated with ISIS, but whose principal goal is getting rid of Assad, don't believe there is a political, diplomatic channel that is ongoing", Mrs Clinton said.

O'Malley interrupted the two higher-polling candidates with a jibe about their respective ages.

"May I offer a different generation's perspective on this?" the 52-year-old governor said, trying to take the attention away from the 74-year-old Vermont senator and the 68-year-old former secretary of state.

He said the US needed to get out of the cold war mentality of who is pro-US and who is pro-Russia.

"We have a role to play in this world," Mr O'Malley said. "But it is not the ... role of travelling the world looking for new monsters to destroy."

Clinton's lead will not have been hurt as she rebuffed attacks from the two men either side of her in an attempt to present herself as the sensible, adult politician in contrast to the republican's inexperienced and volatile Trump.