UNITED NATIONS, April 9 (Xinhua) -- A UN official on Monday called for the establishment of an investigative mechanism for chemical weapons use in Syria after reports of a new chemical attack in the Arab country over the weekend.

"The use of chemical weapons is unjustifiable. Those responsible must be held to account," Thomas Markram, deputy to UN Undersecretary-General for Disarmament Affairs Izumi Nakamitsu, told the Security Council.

At least 49 people were killed and hundreds more were injured in a chemical weapons attack in the rebel-held Douma near Damascus on Saturday, Markram told the Security Council. More than 500 people showed symptoms consistent with a chemical attack, he said.

Markram, who briefed the council last week on chemical weapons in Syria, again called for unity of the council on a dedicated mechanism for accountability for chemical weapons use in the country.

He said the Organization for the Prohibition of Chemical Weapons (OPCW), through its Fact-Finding Mission (FFM), is gathering information about the attack from all available sources. The FFM will report its findings upon completion of its investigation, he said.

The FFM, however, has no power to attribute accountability. A Joint Investigative Mechanism between the OPCW and the United Nations was set up by the Security Council for that purpose. The mechanism, however, ceased to function in November 2017 after Russia blocked the renewal of its mandate.