HELSINKI - Russia and the United States were locked in a high-stakes diplomatic standoff over how to end Syria's bloody civil war Wednesday, as hopes dimmed that crunch talks will be held later this week.
The dispute, which hinges on the fate of Syrian President Bashar al-Assad, could scupper multilateral negotiations scheduled to take place in Geneva on Saturday.
The meeting, brokered by international envoy Kofi Annan aims to find a diplomatic solution to Syria's civil war, which has so far killed an estimated 15,000 people and increasingly threatens regional stability.
Amid a day of frantic telephone diplomacy between capitals, top State Department officials insisted Hillary Clinton would not attend the meeting unless all parties first agreed on the need for political transition in Syria.
"The sticking point is a clear agreement that there needs to be a political transition," said a senior US official late Tuesday, stating that a deal could yet be done.
"Once that is agreed there are a lot of different ways of moving forward from there. What it can't be is just another round of dialogue for dialogue's sake."
Washington, facing a domestic outcry over human rights atrocities committed by the Syrian army, has pressed for an immediate end to the violence and for Assad -- never an ally of the West -- to step down.
"The current regime under Assad has lost legitimacy," said the official.
But jettisoning Assad would signal a major shift in policy for Russia, which has ties to Syria's military and the ruling Ba'ath Party that stretch to the Soviet era.
And US officials said they saw no sign that such a shift had yet taken place.
Russia, which also has a naval base in Syria, has resisted the type of regime change that has swept the rest of the Middle East and North Africa. Moscow was furious with Western powers and NATO for the military operation that ousted Libya's Moamer Kadhafi.
Earlier Tuesday, Russia's veteran Foreign Minister Sergei Lavrov pressed for the meeting to go ahead, but shied away from anything that could smack of outsiders dictating terms to Assad.
"One needs to agree to influence all Syrian sides so that they themselves sit down at the negotiating table and begin to get along and look for consensus solutions," he said.
"Only they themselves can find agreement, and outside players can help them get together."
The Geneva talks had been expected to focus on reviving a peace plan devised by Annan, which has been been rendered moribund by repeated violations of a ceasefire agreement.
Should diplomacy fail, the violence in Syria seems certain to escalate, with uncertain repercussions for the region.
Western powers, along with some Arabian Gulf nations, have reportedly been arming Syrian forces that hope to overthrow the Assad regime, despite doubts about the fighters' motives.
Russia meanwhile has continued to arm Assad's government, further deepening the standoff.
"We think that Russian, or any other, arms sales to the Syrian regime is unhelpful and fuels the conflict," said the senior US official, adding that such actions lent the regime "support and legitimacy."
Clinton will likely raise the issue at a dinner with Sergei Lavrov scheduled for Friday in Saint Petersburg, said the official.
Regional tensions have spiked after Syrian forces shot down a Turkish F-4 jet in the eastern Mediterranean last Friday.
Turkey convened a meeting of NATO allies to discuss the issue and threatened to cut electricity supplies to Syria.
Ankara also warned that further incidents would be met with serious consequences.
Even before the incident, tensions between the two Middle Eastern neighbours had been running high.
Thousands of Syrian refugees have fled across the border to Turkey, while a steady stream of arms for Syrian insurgents had flowed in the opposite direction.
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