Syria slipping from Assad's grasp, White House says

— -- The White House highlighted news reports of high-level Syrian defections and fighting drawing closer to Damascus on Tuesday as signs that President Bashar Assad is "losing his grip" on his country some 15 months into a bloody crackdown on opposition to his rule.

" Recent high-level military defections to Jordan and Turkey are another testament to the regime's loss of control over the situation in Syria," spokesman Jay Carney told reporters aboard Air Force One.

"It is clear, however, that Assad is desperate to hang on to power at all cost, as evidenced by his continued use of air power and Shabiha gangs," who act as enforcers for the regime, Carney said.

President Barack Obama  has expressed frustration over the weak international response to the bloodbath in Syria, where some observers estimate the death toll at 15,000. But efforts to tighten the screws on Assad's regime have foundered on opposition from China and Russia to increased sanctions. Republicans, notably Sen. John McCain, have repeatedly pressed the administration to do more to help Syria's rebels.

Tensions escalated over the weekend when Syrian forces apparently shot down a Turkish reconnaissance jet. Assad's government said it was hit over Syrian territory. The Turks said it had briefly strayed into Syrian airspace but was hit after crossing back into international jurisdiction.

Turkey, a NATO member, took the incident to the alliance's governing body, which condemned Syria but gave no sign of any military response.

Turkish Prime Minister Recep Tayyip Erdogan, in a speech to his party's members in Turkey's parliament,  warned Syria that he has ordered his country's armed forces to respond to any military threat from the regime in Damascus. "The United States and NATO stand in solidarity with Turkey," Carney said. "We will work with Turkey and other partners to hold the Assad regime accountable and to continue to push forward for Syria's needed political transition."

For months, the White House has been insisting that time is not on Assad's side, but that the world needs to do more to hasten his departure. That was the message again on Tuesday.

"Clearly, Bashar al-Assad has been slowly—too slowly—losing his grip over his country," Carney said, charging that "thousands and thousands" of Syrians "have paid for Assad's hubris with their lives."

"That's why we believe it is so essential for the international community to come together and do everything it can to help bring about the political transition that the Syrian people desire and deserve," Carney said.

But he acknowledged that talks with Russia had not yielded a breakthrough.

"There's no question that we have differed on the issue of Syria, but we and the Russians agree entirely that there needs to be a peaceful transition in Syria and end to the violence in Syria," Carney said.

"The United States' view is that that transition cannot include Bashar al-Assad because of the heinous acts that he's perpetrated on his own people," he said.

"He has relinquished any credibility he may have once had, and must step aside so that the Syrian people can build the future that they deserve," Carney said.