After a nearly three-hour meeting in Saint Petersburg, US Secretary of State Hillary Clinton and her Russian counterpart Sergei Lavrov showed just a glimmer of hope that a deal could be done to help end the bloodshed.
Describing the meeting, a senior US official said there remained areas of "difficulty and difference" between Russia and the United States over the political future of the war-ridden nation.
But both powers agreed to continue talks in Geneva on Saturday, where they will be joined by other permanent members of the UN Security Council and a handful of regional powers.
"Out of respect to (international peace envoy) Kofi Annan, they agreed we should all go to Geneva tomorrow to try to produce a result," the US diplomat said.
Clinton had threatened to boycott the meeting if Russia did not agree to Annan's plan for political transition, which included an opaque but unmistakable call for Bashar al-Assad and his government to be replaced by a government of national unity.
Buoyed by the removal of that US threat, Lavrov voiced optimism that Saturday's talks could bring a shift toward peace after 16 months of fighting.
Russia's top diplomat said he had now "detected a shift" in Washington's approach.
"There were no ultimatums. Not a word was said about the document now being discussed in Geneva being completely untouchable."
"I can confidently say that we have a very good chance tomorrow in Geneva to find a common denominator and mark a path forward," he told reporters.
Russia -- long an ally of Syria -- has argued that foreign powers should not dictate terms to Syria and has provided its old ally with weapons.
Russia's Deputy Foreign Minister Gennady Gatilov early on Saturday tweeted that experts in Geneva had thus far failed to agree to the wording of a final document on Syria because "the Western partners want to determine the political process themselves."
UN-Arab League envoy Annan said "external powers" have encouraged violence in Syria as he issued a new plea for unity ahead of the key international meeting on the conflict on Saturday.
"Many external powers are deeply involved. Despite formal unity behind the six-point plan, mutual mistrust has made them work at cross-purposes," Annan said in a commentary for the Washington Post published Friday.
Meanwhile fighting has only intensified in recent weeks and rights monitors said more than 230 people -- most of them civilians -- had been killed across the strategic Middle East country since Thursday.
Regime forces pounded the Damascus suburb of Douma and the central city of Homs on Friday, after one of the bloodiest days of the Syrian uprising in which more than 180 people were thought to have been killed.
Other demonstrations calling for the ouster of President Assad took place in Aleppo, Daraa, Deir Ezzor, Idlib, Homs and Latakia provinces.
Meanwhile Turkey has sent tanks, troops and missile batteries toward the Syrian border, after Syria shot down a Turkish jet last Friday.
Turkish state-run television showed dozens of military vehicles reportedly heading for the border, in a convoy that included air defence systems.
The head of the rebels' Free Syrian Army told AFP that 2,500 Syrian soldiers were "massing 15 kilometres or slightly more (10 miles) from the Turkish border" on Friday.
A Syrian foreign ministry spokesman did not deny the report when contacted by AFP while stressing there were "no hostile intentions from the Syrian side."
The United States and regional powers such as Turkey are under pressure not only from Russia but also members of the rebel resistance themselves.
The Syrian National Council has expressed grave reservations about any transition process that reserves a role for Assad.
French Foreign Minister Laurent Fabius was to hold Paris talks with rebel council chief Abdel Basset Sayda in hopes of persuading him to take a more accommodating line.
The London-based Syrian Observatory for Human Rights said some 4,700 of the more than 15,800 people killed since the uprising broke out had died since the UN-backed ceasefire brokered by Annan entered force.