British Prime Minister David Cameron said on Thursday it was "unthinkable" that Britain would launch military action against Syria to punish and deter it from chemical weapons use if there was strong opposition at the United Nations Security Council. "It would be unthinkable to proceed if there was overwhelming opposition in the UN security council," Cameron told parliament, when asked if Britain would press ahead with action if there was strong opposition at the United Nations. He also said that there would not be any British action on Syria until UN weapons inspectors report, and a vote in the parliament. He said that he was convinced the Syrian regime was behind a chemical weapons attack, but admitted there was no "100-percent certainty".