Defections, fighting closer to Damascus and the downing of a Turkish jet are all signs that Syrian President Bashar al-Assad's regime is losing control, the United States said Tuesday.
Speaking on board Air Force One as President Barack Obama flew to a re-election campaign event in Georgia, White House spokesman Jay Carney particularly noted recent "high-level defections."
"Clearly Bashar al-Assad's regime has slowly been losing its grip on its country," Carney told journalists, repeating US condemnation of Syria's "unacceptable" shooting down of a Turkish fighter jet.
UN-Arab League envoy Kofi Annan is trying to convene a meeting of foreign ministers from the major powers in Geneva on Saturday to discuss political efforts to implement his floundering six-point peace plan.
The United States will continue to pursue a political transition that does not include Assad remaining at the helm, Carney said, specifying: "Our view is that the transition cannot include Assad."
The downing Friday of the Turkish jet triggered a chorus of international condemnation as well as appeals for restraint to prevent a military escalation of the Syria conflict, which is now in its 16th month.
A Turkish diplomat, meanwhile, told AFP that one Syrian general, two colonels and five other army officers including two majors, accompanied by 24 family members, crossed into Turkey late on Sunday.
The latest defections brought to 13 the number of generals seeking refuge in the country since the revolt against the government of Assad erupted in mid-March 2011.
The violence has killed more than 15,000 people, the Syrian Observatory for Human Rights says.
Carney described the loss of life as "horrific" and accused Assad of "hubris."
It is "essential for the international community to come together" to work towards a political transition in Syria, the White House spokesman said.
Russia is pushing for an international Syria conference and has already discussed the plan with Jordan as well as the European Union, Iran and Iraq.
President Vladimir Putin's strident rhetoric and a flat-out refusal to support sanctions against Moscow's Soviet-era ally Syria have pitted him against the West.
"We've had very productive meetings" with Russia, Carney said, but added: "There's no question we have differences." The US has opposed Iran's involvement in any international meetings on Syria.