PARIS - As a Syrian general who was a personal friend of Bashar al-Assad fled for France, Hillary Clinton urged Assad's enemies meeting in Paris on Friday to make Russia and China "pay a price" for helping keep him power in Damascus. The Secretary of State's remark, among Washington's toughest yet in 16 months of revolt, highlighted the gulf between Western and Arab countries, who met opposition groups in Paris to try to engineer Assad's departure, and his two supporters on the other side of the old Cold War divide, who stayed away from the talks. "I will tell you very frankly," Clinton told the Friends of the Syrian People conference, "I don't think Russia and China believe they are paying any price at all - nothing at all - for standing up on behalf of the Assad regime. The only way that will change is if every nation represented here directly and urgently makes it clear that Russia and China will pay a price because they are holding up progress - blockading it. "That is no longer tolerable." The foreign ministers and senior diplomats from 50 Western, Arab and other countries - including Assad's former ally and neighbor turned bitter foe Turkey - urged stronger U.N. Security Council action and "broader and tougher" sanctions. They also agreed to "massively increase" aid to Syria's rebels and to provide them with communications equipment, according to a final statement. Western powers are reluctant to offer much greater firepower to rebels whose ranks include anti-Western Islamists. Divisions among Assad's foes, visible notably in a fistfight at an opposition meeting in Cairo this week, have also limited the coordination of efforts to remove him by force. As Clinton spoke, Manaf Tlas, a brigadier in the Republican Guard who attended military college with Assad and whose father was Assad's father's confidant and defense minister for 30 years, was on his way to Paris, the French government said. There was no immediate sign that Tlas, who friends said had fled Damascus for Turkey this week, would throw in his lot with the rebels. He did not attend Friday's meeting. But his defection was the clearest signal yet that some in Assad's inner circle think his days in power are numbered, as an uprising that began in March 2011 with a groundswell of peaceful protest turns into a civil war with strong sectarian overtones. Tlas's father Mustapha now lives in Paris, as does Tlas's sister. The family has been a rare representative of Syria's Sunni Muslim majority in an elite dominated by Assad's fellow Alawites. Sunnis have been in the forefront of the uprising. Assad's enemies among Syrians and in the West were quick to hail Tlas's flight as a breakthrough, while Damascus played it down. A Syrian news website quoted a Syrian official on Thursday as saying: "His desertion means nothing ... If Syrian intelligence had wanted to arrest him it would have." Opposition sources have spoken of senior figures who are under suspicion of being potential defectors being held under virtual house arrest. Assad's opponents have been trying to encourage as many of his entourage as possible to abandon him. While the lightly armed rebels are no match for Syria's large and well-equipped army, their hope lies in eroding loyalty and conviction within Assad's establishment to the point where it loses its hold on power. Syria's army took control of the rebel stronghold of Khan Sheikhoun in northern Idlib province on Friday after an assault on the town backed by helicopters, rebels said. "The Free (Syrian) Army withdrew from the town last night after it ran out of ammunition. Assad's army is in control," said Abu Hamam, a rebel spokesman who fled to a nearby village. "They are burning the houses. They have burned my own house. I see the smoke covering the sky from where I am now." Army shelling and assaults also killed three people in the southern province of Deraa, where the nationwide revolt began. Opposition activists say more than 15,000 people have been killed in the uprising, while the government says several thousand members of the security forces have died. The host of the Paris meeting, French President Francois Hollande, said Assad's departure was "in the interest of Syria, of its neighbors and everybody who wants peace in the region".