PARIS — Opponents of President Bashar al-Assad of Syria met here on Friday with their international sponsors to intensify pressure for his removal, buoyed by word that Brig. Gen. Manaf Tlass, a commander in the elite Republican Guard, and a member of the Damascus aristocracy, had defected and fled the country.

French Foreign Minister Laurent Fabius told the meeting that a “senior official” and commander of the Republican Guard had “defected and is on his way to Paris.” Ministry officials confirmed that Mr. Fabius was referring to General Tlass but did not say whether the Syrian general would join the talks. The number of high-ranking officers quitting Mr. Assad’s forces has increased markedly in recent days as violence has mounted, but the departure of General Tlass was the first from within the gilded circle around the president since the uprising against him began in March 2011, representing the kind of embarrassing departure long anticipated to indicate that the government’s cohesion was cracking.

Not only is General Tlass a close friend and contemporary of President Assad, he is also part of a powerful dynasty dating to the days when his father, Gen. Mustafa Tlass, was defense minister from 1972 to 2004, acting as a key ally of Hafez al-Assad, the father of the current Syrian leader, as he created the repressive system that controls the country.

As the gathering of more than 100 countries opened, Secretary of State Hillary Rodham Clinton called for increased pressure on Syria to implement a proposal for a transitional government agreed at a separate meeting among outside powers in Geneva last weekend. But, many analysts argue, the diplomatic effort is rapidly being overtaken by events on the ground, including the defections of high-ranking military officers and ever greater bloodletting.