Donald Trump administration will 'fully implement' US obligations on Iran nuclear deal: National Security Advisor

The Donald Trump administration will "implement fully" all existing US obligations under the Iranian nuclear deal, National Security Advisor H R McMaster on Sunday said.

"What the president, though, has done is he has set out a marker, a marker to Iranians and to our allies and partners that we have to fix fundamental flaws in this deal," McMaster told Fox News in response to a specific question on the issue.

The Iranian nuclear deal is a "weak deal" that is being "weakly" monitored, he said.

As such President Donald Trump has made clear that he will not permit this deal to provide cover for what is "a horrible regime" to develop a nuclear weapon, he said.

McMaster said one of the problems with this deal is that the US can't really say with confidence that the Iranians are complying.

"We know from their behaviour, their behaviour broadly in the region, and their behaviour within the agreement where they have walked up to the line, they have crossed the line several times in terms of the restrictions, that this is not a trustworthy regime. So, much more comprehensive monitoring is in order," he said, adding, the US is seeking implementation of the deal.

"It's just to implement the agreement by going to sites, to fully implement the inspections of sites, the monitoring of suspicious sites within Iran," he said.

Iran he said has to revisit it because otherwise "what you do is you just give the Iranians the opportunity" to develop the nuclear capability, he said.

"Their programmes can advance and then they can go to industrial scale enrichment of uranium within a very short period of time and then bridge into a weapon, and that is just an unacceptable risk in the world," he added.

He said Trump is not walking away from the deal just yet.

"So, if he sees some real change, if he sees the ability of the Congress within US law to address some of these problems associated with the deal. In our legislation, the domestic law about the deal was really flawed because it was really just about cost reporting to each other," he said.

Trump has asked Congress help fix this domestic legislation and work on as Secretary of State Rex Tillerson has said, a deal that can lay alongside the Joint Comprehensive Plan of Action (JCPOA) and address its fundamental flaws, he said.

Trump has laid out a strategy for dealing with Iran's destabilising and dangerous hate filled behaviour, its behaviour toward its own people and its behaviour towards the region, he said.

McMaster also said Trump will not allow North Korea to threaten the US with a nuclear weapon.

"Our president has been really clear about this. He is not going to permit this rogue regime, Kim Jong-un, to threaten the United States with a nuclear weapon," he said.

Trump is willing to do anything necessary to prevent that from happening and North Korean leader Kim Jong-un should recognise this if he thinks the development of this nuclear capability is keeping him safer, he said.

"It's actually the opposite. It's having the opposite effect," he said noting that the options available with the US including the military one are constantly under refinement.

"We have a broad range of new capabilities coming into our armed forces, thanks to the president's focus on modernising the armed forces, addressing what had been a bow wave of deferred military modernisation," he said, adding the military are refining, improving plans every day.

"Plans we hope we don't have to use but we must be ready, we have to be ready. And so, all of our armed forces are getting to really a high, high degree of readiness for this mission, if it's necessary," McMaster said.

Responding to a question, he said Kim Jong-un doesn't understand how serious the US is about his behaviour and the behaviour of his regime.

"The president has been very clear on that and I think it's beneficial to the safety and security of not only the United States but our great allies in South Korea and Japan and the world," the national security advisor said.