"They claim to represent the Syrian people. If you want to speak in the name of the Syrian people, you should not be traitors to the Syrian people, agents in the pay of enemies of the Syrian people," Muallem said in a strongly-worded speech as the meeting got under way in the lakeside city of Montreux.
He fired a broadside at the reform-shy Gulf monarchies which back the revolt against the regime of Syrian President Bashar al-Assad, which began after a crackdown on peaceful Arab Spring-inspired protests in 2011 and has morphed into a sectarian war.
"It is regrettable to me and to the people of Syria that representatives of states in this room are sitting with us today, while blood is on their hands -- countries that have sent weapons ... encouraged and financed terrorism," Muallem said.
"They have not looked at their own glass houses before throwing stones," he said.
"The mask has fallen and we can see the real face of what they want -- to destabilise Syria .. by exporting terrorism -- to hide their barbaric behaviour," he thundered.
Syria slams the role of foreign Sunni Islamist fighters who have flocked to the war-torn country -- though Assad is backed by Shiite Iran and its Lebanese ally Hezbollah -- and says it is locked in a "war on terror".
"Who told you that Syria wants to go back 1,000 years," he said, warning against extreme Islamism.
"It will not stop in Syria," he said.
He singled out Turkish Prime Minister Recep Tayyip Erdogan for backing the opposition.
"All of this would not have happened if it had not been for Erdogan -- they did not know that magic would turn against the magician one day -- terrorism has no religion," he said.
Muallem also rebuked US Secretary of State John Kerry, who told the conference there would be no place for Assad in a future government.
"No one in the world has the right to confer or withdraw the legitimacy of a president, a constitution or a law, except for the Syrians themselves," Muallem said.
Muallem also locked horns with UN Secretary General Ban Ki-moon, the conference chairman, who had asked delegations not to trade barbs and to respect time limits imposed on all speeches.