Democratic frontrunner and former US Secretary of State, Hillary Clinton has said she is "very proud" of the Iranian nuclear agreement and its compliance by Tehran even though she thinks there is still need to "carefully watch" Iran.

"I'm very proud of the Iran nuclear agreement. I was very pleased to be part of what the president put into action when he took office. I was responsible for getting those

sanctions imposed which put the pressure on Iran. It brought them to the negotiating table which resulted in this agreement," Clinton said during a Democratic party's presidential debate.

"And so, they have been so far, following their requirements under the agreement. But I think we still have to carefully watch them. We've had one good day over 36 years and I think we need more good days before we move more rapidly toward any kind of normalisation," Clinton said.

"We have to be sure that they are truly going to implement the agreement. We have to go after them on a lot of their other bad behaviour in the region which is causing enormous problems in Syria, Yemen, Iraq and elsewhere," she said.

Responding to a question on Syria, Clinton said her plan does not include American troops on the ground.

"It includes the United States leading an air coalition which is what we're doing, supporting fighters on the ground; the Iraqi Army which is beginning to show more ability, the Sunni fighters that we are now helping to reconstitute and Kurdish on both sides of the border," she said.

"We also have try to disrupt their supply chain of foreign fighters and foreign money and we do have to contest them in online space. I'm very committed to both going after IS but also supporting what Secretary Kerry is doing to try to move on a political diplomatic to try to begin to slow down and hopefully end the carnage in Syria which is the root of so many of the problems that we seen in the region and beyond," Clinton said.

Clinton's main rival in the race to bag the Democratic presidential nomination, Bernie Sanders said the vacuum in the Middle East was created by the disastrous war in Iraq, which he vigorously opposed.

"You have incredibly wealthy countries in that region, countries like Saudi Arabia, countries like Qatar. Qatar happens to be the wealthiest country per capita in the world. They have got to start putting in some skin in the game and not just ask the United States to do it," he said.

"Our first priority (in the region) must be the destruction of ISIS. Our second priority must be getting rid of Assad, through some political settlement, working with Iran, working with Russia," Sanders said.

"But the immediate task is to bring all interests together who want to destroy ISIS, including Russia, including Iran, including our Muslim allies to make that the major priority," he said.