Western and Middle Eastern backers of Syria's weakened opposition gather in Paris Saturday to discuss a ceasefire, having watched the conflict turn decisively in favour of Syrian President Bashar al-Assad and Russia.

Foreign ministers from Europe, US Secretary of State John Kerry and their counterparts from Qatar and Saudi Arabia are likely to renew what have been so far ineffective calls for an end to the onslaught on Aleppo.

Opposition-held areas of the city, home to hundreds of thousands of civilians, have been starved in a siege and pummelled by an offensive by Syrian forces backed by Iranian militias and Russian airpower.

Retreating rebels now control only a pocket of Syria's second city, whose fate is seen as pivotal to the outcome of a nearly six-year-old war that has killed more than 300,000 people.

Calls from Western leaders to stop the fighting and diplomacy at the UN have so far amounted to nothing with Assad and Russian President Vladimir Putin seemingly intent on pushing their advantage.

The talks on Saturday, which will also include Turkey, the United Arab Emirates and Jordan, will focus on getting the warring parties back to the negotiating table for talks in Geneva.

"My goal in all this is... to get both sides, all of the forces, to the table in Geneva. And that's what we're working on," Kerry said as he arrived on Friday night. 

Russian and American officials will meet again in Geneva on Saturday to discuss the fighting, but even Kerry struggled to sound optimistic about an outcome.

"I know people are tired of these meetings, I'm tired of these meetings," he told reporters. 

"But what am I supposed to do? Go home and have a nice weekend in Massachusetts, while people are dying? Sit there in Washington and do nothing?"

Analysts say the timeframe and conditions of talks will be set in Damascus and Moscow, whose armies are in the ascendency despite allegations of war crimes and mounting civilian deaths.

"Aleppo is a critical turning point," Robin Wright, a researcher at the United States Institute of Peace, told US National Public Radio (NPR). "Assad looks ever stronger."

She said the rebels which have been armed and financially backed by the countries gathered in Paris now have "very diminished chances of being a viable alternative" to the Syrian regime.

- Assad or extremists? -

Joshua Landis, director of the Center of Middle East Studies, also called Aleppo "a major turning point" that left the West and other countries which oppose Assad with few allies.

Once the city falls, the largest remaining rebel bastion will be Idlib province, controlled by a coalition dominated by extremists from a former Al-Qaeda affiliate. 

The Islamic State jihadist group remains in control of territory around their de facto capital in Raqa.

"It makes the prophecy of Assad come true: it is either me or radical Islamists," Landis told NPR.

The election of Donald Trump in the United States, who favours closer relations with Putin, was already a bad omen for the opposition just before troops launched their assault on Aleppo in mid-November.

Trump is expected to be more isolationist than Barack Obama, which Moscow-based analyst Pavel Felgenhauer said would allow Russia to strengthen its position in the Middle East.

"Everyone is going to be queuing up to become friends with Russia," said Felgenhauer, a defence analyst who writes for the independent newspaper Novaya Gazeta

"Everyone understands that Assad could have been hanged a long time ago. But he bet on the Russians and he won," he told AFP.

- Assad's future crucial -

But when Aleppo does fall, the Syria conflict is far from over, with extremists from al-Nusra and IS, as well as US-backed Kurdish militias in the north, in control of large swathes of the country.

The US and Russia have special forces on the ground, while Turkey has regular troops inside Syria near its border. The skies buzz with planes from Russia and a US-led coalition of Western and Arab nations.

"If Assad takes over Aleppo, is the war going to end? No. Will he have solved the political challenge of bringing people together to unite the country? No," Kerry said on Tuesday.

The US and Europe insist that a political settlement in which Assad agrees to step down is necessary to end the fighting and then rebuild the shattered country.

Multiple rounds of talks between the regime and the opposition over the last two years came to nothing.

Source: AFP