UN's special envoy to Syria Lakhdar Brahimi said on Wednesday that evidence suggests that some kind of chemical substance was used in Syria that may have killed more than 1,000 people,but any military strike in response must first gain UN Security Council approval. Brahimi spoke to reporters in Geneva as a UN inspection team was investigating the alleged poison gas attack near Damascus on August 21 and momentum built for Western military action against Syrian President Bashar Assad's regime in the civil war that he called the most serious crisis facing the international community. "With what has happened on the 21st of August last week,it does seem that some kind of substance was used that killed a lot of people: hundreds,definitely more than a hundred,some people say 300,some people say 600,maybe 1,000,maybe more than 1,000 people," Brahimi said. "This was of course unacceptable. This is outrageous. This confirms how dangerous the situation in Syria is and how important for the Syrians and the international community to really develop the political will to address this issue seriously,and look for a solution for it," he said. Brahimi did not elaborate on whether he based his information on the work of the UN team or other sources such as western intelligence,including what US Secretary of State John Kerry has called "undeniable" evidence of a large-scale chemical attack likely launched by Assad's regime. Brahimi also said that any US-led military action must first gain approval from the 15-nation Security Council,whose five permanent members Britain,China,France,Russia and the United States each have veto power. "International law says that any military action must be taken after" Security Council approval,he said. But,he added,President Barack Obama's administration is "not known to be trigger-happy." Meanwhile,UN Secretary General Ban Ki-moon called for the divided Security Council to unite and said that the horrors in Syria cannot be seen in silence,and the world's mediatory body must do its utmost to draw representatives of concerned parties in the conflict to the negotiations table. Calling the situation in Syria the 'biggest challenge to war and peace'in the world in the present day,he urged for the UN chemicals expert team to be given more to determine their findings and called upon all states to withhold from supplying arms to either Assad's forces or the rebels,saying that such a move would only promote further fighting and lead to more bloodshed.