Syria's Assad must be held accountable for chemical attacks, says Trump adviser

H.R. McMaster made the call on Saturday in a speech at the Munich Security Conference, in the latest warning to Syrian President Bashar al-Assad over the use of chemical weapons.

"It is time for all nations to hold the Syrian regime and its sponsors accountable for their actions and support the efforts of the Organisation for the Prohibition of Chemical Weapons," McMaster said.

"Public accounts and photos clearly show that Assad’s chemical weapons use is continuing," he added.

According to Washington, at least six chlorine attacks have been reported in Syria since early January in rebel-held areas, resulting in dozens of injuries.

The Syrian government on Wednesday denied it possessed chemical weapons and branded the use of such arms "immoral and unacceptable".

The denial came after a French warning of punitive strikes if proof emerged that the Syrian regime had used banned chemical weapons against its civilians.

The Syrian regime has repeatedly been accused of using chemical weapons, despite a 2013 deal between the US and Russia for Damascus to destroy its stockpiles.

The United Nations was among those who blamed government forces for an April 2017 sarin gas attack on the opposition-held village of Khan Sheikhun that left scores dead.

In retaliation for that alleged attack, the US carried out cruise missile strikes on a Syrian regime airbase.

Next month the war in Syria will enter its eighth year with diplomatic efforts stalled as violence rages on the ground.