"The horrific events of yesterday demonstrate unfortunately that war crimes are going on in Syria [and that] international humanitarian law is being violated frequently," Antonio Guterres told reporters in Brussels ahead of a conference on the future of Syria.

The UN chief added that he was “confident that the Security Council will live up to its responsibilities” at its emergency meeting Wednesday.

EU foreign policy chief Federica Mogherini also stressed the need for joint action to stop the violence and war in Syria.

"It's a day when the multilateral approach is more needed than ever," she told reporters when welcoming Guterres to EU headquarters.

Representatives from 70 countries and some international organizations gathered in Brussels to discuss the future of Syria.

 "All the evidence I have seen suggests this was the Assad regime who did it in the full knowledge that they were using illegal weapons in a barbaric attack on their own people," said British Foreign Secretary Boris Johnson. 

 He added the "barbaric regime” in Syria has no legitimacy to govern the country.

 German Foreign Minister Sigmar Gabriel called on Russia to support a possible new UN Security Council resolution against the Syrian regime.

 "We find it right that the United Nations Security Council should be occupied with this case of poisonous gas today. We appeal to Russia to support this Security Council resolution, to investigate the incident, and to hold to account those responsible," he said.

 "Of course, we should do everything to bring those responsible to an international court because it is one of the most evil war crimes you can imagine," he added.