Hundreds of innocent people have been killed in spectacular attacks claimed by Islamic State militants from Syria, but diplomats say major powers are no closer to a peace deal to end nearly five years of bloodshed and chaos there.

Meeting in Vienna the day after Friday night's Paris attacks, Russia, the United States and powers from Europe and the Middle East agreed on a two-year timeline leading to Syrian national elections that left many questions unresolved.

On the surface, the talks on Syria appeared to narrow the gap that divides Russia, which like Iran supports Syrian President Bashar al-Assad, and the West, which wants Assad out.

The attacks that killed 129 people in Paris, the bombing of a Russian airliner that claimed more than 200 lives and deadly attacks claimed by Islamic State in Lebanon and elsewhere have boosted the resolve of major powers to crush the militants.

Russia, the United States and their allies in Europe and the Middle East all back U.N.-mediated talks between the Syrian opposition and government and favour a unity government in Syria within six months leading to elections 18 months later.

But beneath the surface, major rifts remain.

"You would think that these tragedies would bring us closer to a peace deal, but no," a senior Western diplomat said on condition of anonymity. "The Russians and Iranians are more convinced now that Assad is the only hope for Syria ... But we know that Assad is the problem, not the solution."

The diplomat's sentiments were echoed by other Western and Arab diplomats familiar with the closed-door Vienna talks. They cited furious exchanges between Iran and Saudi Arabia, which back opposing sides in the Syrian conflict, and said cooperation between those two rivals appeared all but impossible.

One Western diplomat said the Saudis "were dragged kicking and screaming to the Vienna talks." Others said it was Washington that pushed a reluctant Riyadh to attend.

"In public, people talk about how the Paris attacks changed everything," another diplomatic source told Reuters. "But there's little, if anything, that's been agreed on Syria."

Left unanswered is the crucial question of whether Assad has a future in Syria. U.N. special envoy on Syria Staffan de Mistura told Austria's Kleine Zeitung newspaper Assad's fate was an issue on which the powers in Vienna "agreed to disagree."

CEASEFIRE?

While willing to tolerate Assad for a time during a transition period, Western and Gulf Arab powers say he must step aside. Russia and Iran say the decision must be left to Syrians - a position Western officials say would mean Assad stays.

Russia blames the West for the persistent deadlock. On Wednesday Foreign Minister Sergei Lavrov said if the West wants an international coalition against Islamic State, it must drop its demands for Assad's ouster.

Saturday's announcement from Vienna said the five permanent Security Council members would support a Syria ceasefire resolution. Council diplomats said work on it has yet to begin.

British U.N. Ambassador Matthew Rycroft told reporters he expected it would take "weeks, not days" to draft a resolution establishing a ceasefire monitoring mechanism. Other council diplomats said it could take months.

A key issue for a ceasefire will be determining which groups fighting Assad will be branded moderate opposition fighters deserving of a seat at the negotiating table and which will be labelled terrorists. That task has been assigned to Jordan.

Opposition groups deemed legitimate will be invited to take part in the ceasefire while those labelled terrorists will be treated as fair game for Syrian government forces, Russia, the United States, France and others conducting air strikes in Syria.

U.S. Secretary of State John Kerry has repeatedly said that any ceasefire would not apply to Islamic State militants and al Qaeda, which would continue to be the target of Western strikes.

Assad and Russia have tended to view anyone opposed to Assad as a terrorist. Like Russia, Iran has provided generous military support to Damascus and is standing by Assad.

"We support Assad because he is the only one who can protect Syria's integrity," a senior Iranian official said, reaffirming that the Paris attacks had failed to break the political deadlock on Syria. "Instead of weakening Assad, we should support him in his fight against all terrorist groups in Syria."

In an interview with Italy's Rai 1 television broadcast on Wednesday, Assad said "defeating terrorism" must come before deciding any transition timetable. Once that is done, he said, 18 months to two years is enough for a transition.