Syrian children and adults receive treatment for a suspected chemical attack at a makeshift clinic on the rebel-held village of al-Shifuniyah in the Eastern Ghouta region on the outskirts of the capital Damascus on Feb. 25, 2018. (Xinhua/AFP)

UNITED NATIONS, March 21 (Xinhua) -- Concerned by the persistent allegations of chemical weapon use in Syria, United Nations (UN) Secretary-General Antonio Guterres Wednesday reiterated his call for the UN Security Council to demonstrate unity and resolve on the issue.

"The use of chemical weapons, under any circumstances, is unjustifiable and abhorrent. Equally unjustifiable is a lack of response to such use, if and when it occurs," Stephane Dujarric, his spokesperson, said. "Impunity cannot prevail with respect to such serious crimes."

Guterres was referring to the Security Council's failure to renew the mandate of a joint investigative mechanism of the UN and the Organisation for the Prohibition of Chemical Weapons (OPCW) in November.

The mechanism, which was authorized by the Security Council to determine who were using chemical weapons in Syria, had to be disbanded after Russia vetoed extending its mandate.

Russian Ambassador to the United Nations Vassily Nebenzia speaks after the UN Security Council failed to adopt Japan's draft resolution to extend 30 days for mandate of mechanism investigating chemical attacks in Syria, at the UN headquarters in New York, Nov. 17, 2017. The UN Security Council failed to adopt the resolution extending 30 days for mandate of mechanism investigating chemical attacks in Syria on Friday. (Xinhua/Li Muzi)

Guterres met OPCW Director-General Ahmet Uzumcu Tuesday and reiterated his support for the organization's work in investigating allegations of chemical weapon use in Syria.

Uzumcu was in New York to brief the Security Council on the issue, including the destruction of Syrian chemical production facilities as well as the government's declaration of its chemical weapon stockpiles and facilities.

After the closed-door meeting of the Security Council, Uzumcu said there are several new allegations of chlorine attacks in Syria.

In this file photo taken on April 7, 2017, Syrian residents of Khan Sheikhun hold placards and pictures during a protest condemning a suspected chemical weapons attack on their town that killed at least 86 people, including 30 children, and left hundreds suffering symptoms including convulsions, vomiting or foaming at the mouth. (Xinhua/AFP)

The OPCW Fact-Finding Mission in Syria is looking into the alleged incidents, some of which are attributed to the Syrian Government and others to armed opposition groups, he told reporters.

There are also allegations of chemical weapon use in the northern Syrian district of Afrin, where Turkish forces are launching attacks on Kurds. But the OPCW mission could not find credible information to pursue an investigation,Uzumcu said.