The United States has sanctioned 271 Syrian government employees in response to Bashar Assad's alleged use of chemical weapons.

The move marks one of the largest sanction actions in US history and means American companies are banned from doing business with any of the workers.

The US is responding after least 80 people, including children, were killed in a rebel-held town in northern Syria on 4 April.

Nato have accused the Syrian President of gassing his own people in the attack on the town of Khan Sheikhoun.

The British government said earlier this month that tests in the UK confirmed that sarin or a "sarin like substance" had been used in the suspected gas explosion.

The sanctions have been placed on employees at Syria's Scientific Studies and Research Centre, the Syrian government agency responsible for developing and producing non-conventional weapons.

President Assad, denying the western accusations, said his forces had already given up its chemical arsenal and claimed the reports of the deaths may have been faked to justify the US's retaliatory airstrikes in the country.

He suggested the attack may not have taken place at all and said people - including children - seen dead in photographs might have been play acting.

"There was no order to make any attack. We don't have chemical weapons - we gave up our arsenals a few years ago," he said during an interview with French news agency AFP.

The action was announced in a statement by the Treasury Department, and Treasury Security Steve Mnuchin simultaneously briefed reporters at the White House.

The US retaliated earlier this month by launching missiles against a Syrian airfield.

On Monday US President Trump urged the UN to take action against North Korea's threatening attitude and towards the situation in Syria.

He called on other members of the United Nations to do more in terms of sharing the "burden militarily and financially."