A UN inquiry showed that Damascus used chemical weapons, Erler said in an interview published on Thursday.

"The findings are unambiguous," he told the daily "Neue Osnabrücker Zeitung."

However, Russia was still backing the Syrian government in the UN Security Council debate on international response.

"Moscow is obviously more concerned about being seen as a friend of the criminal Assad regime than in taking joint action and sanctions against this provocative treaty violation," Erler told the paper. "Every criticism of this behavior is justified."

'No fingerprints on the gun'

Earlier, United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) reported that the regime troops used chlorine gas against civilians on at least two occasions. The gas containers were allegedly dropped from Syrian air force helicopters.

The investigators also said the "Islamic State" group also used mustard gas in an attack. Chemical weapons were used in several more incidents, but investigators were not always able to determine the responsible side, according to the UN report.

Russia's UN representative, Vitaly Churkin, said the document still presented "many open questions" before it could be accepted. The report presented "no names, no details, no fingerprints," he said.

"Clearly there is a smoking gun. We know that chlorine was most likely used, but there are no fingerprints on the gun," the Russian diplomat told reporters.

Syrian UN ambassador, Bashar Ja'afari, dismissed the report's findings as biased.

"The conclusions contained in the report were totally based on statements made by witnesses presented by the terrorist armed groups," he said. "Therefore, these conclusions lack any physical evidence."

Amnesty disappointed

In the Thursday interview, Erler said the UN Security Council was putting its credibility on the line in Syria. In the past, veto-wielding members Russia and China blocked several resolutions aimed against the Syrian regime.

"The United Nations should prepare clear sanctions, despite the Russian veto threat," the German official told the newspaper.

He also said Moscow needed to decide if it wanted to risk international isolation over the issue.

Amnesty International also criticized Russia for preventing the UN from being able to draw "consequences" from the presented evidence.

"It is disappointing that the UN Security Council is still incapable of action in Syria," Amnesty's Rene Wildangel told the "Neue Osnabrücker Zeitung."

Syria officially agreed to hand over all its chemical weapons in 2013, under a deal brokered by the US and Russia.

dj/sms (Reuters, AFP)