Embattled Syrian President Bashar al-Assad has attacked Donald Trump saying the Republican candidate for the White House has insufficient foreign policy experience to lead the country, comparing the GOP nominee to the previous three US presidents.

Asked in a NBC interview whether he thought a Trump presidency would be "dangerous" for the country Assad said the former reality star would inevitably pose a threat, claiming past US presidents had been similarly inexperienced.

"Who had this experience before? Obama? Or George Bush? Or [Bill] Clinton before? None of them had any experience," he said. "This is the problem with the United States."

In a possible gesture to Trump's Democratic opponent Hillary Clinton, Assad said having had "a few years" experience in foreign affairs also wasn't enough. "Of course it is dangerous for the country generally," he asserted.

In the wide ranging interview, Assad, whose 16-year-long presidency has been dominated by Syria's cataclysmic five-year war, also answered questions on his regime's relationship with Russia and the death Sunday Times journalist Marie Colvin in 2012.

Assad told the US news programme he had never been asked by Russian President Vladimir Putin to step down. "They never said a single word regarding this," he said.

Moscow has been the foremost guarantor of the Syrian regime in Damascus alongside Iran. Russian intervention into the war in Syria in September 2015 has been viewed as one of the principle reasons for Assad being able to cling to power.

Colvin's family has filed a lawsuit against the Syrian government over her death during regime air strikes over the city of Homs in February 2012. They have said they have direct evidence Assad was targeting Colvin and her colleagues in the then rebel-held city.

"Nobody knows if she (was) killed by missile, or which missile, and where did the missile come from, or how. No one has any evidence," Assad claimed before adding Colvin had entered Syria illegally and "went with the terrorists".

Assad Syria
Assad's 16-year-long presidency has been dominated by Syria’s cataclysmic five-year warReuters