Hillary Clinton is not 'qualified to be president'

US presidential candidate and self-styled Democratic Socialist Bernie Sanders said his opponent and front-runner Hillary Clinton was not "qualified" to be president.

"Secretary Clinton appears to be getting a little bit nervous," he told a crowd in Philadelphiaon Wednesday.

"And she has been saying lately that she thinks that I am 'not qualified' to be president. Well, let me, let me just say in response to Secretary Clinton: I don't believe that she is qualified."

Sanders beat Clinton with 54 percent to 46 percent on Tuesday during the Wisconsin presidential primary on Tuesday.

The win in Wisconsin will also allows Sanders to make the case to "super-delegates", who can make up their minds about whom to support.

After Wisconsin, the next state to vote in the primaries to elect the Republican and Democratic candidates for the November presidential election is New York, where voters will go the polls on April 19.

Sanders, during his speech went on to turn that critique back on the former secretary of state.

"I don't think you are qualified if you have voted for the disastrous war in Iraq. I don't think you are qualified if you have supported virtually every disastrous trade agreement which has cost us millions of decent paying jobs," he said.

The two candidates will face off in a debate in New York on April 14, hosted by TV channels CNN and NY1.