MUNICH (Reuters) – Major powers began a new round of Syria talks on Thursday focusing on calls for a ceasefire and access for aid, but the mood was dour with Moscow showing no sign of calling off its bombing in support of a massive new government advance.

With the Syrian opposition saying it cannot accept a truce because it does not trust the Russians, diplomats saw little chance of progress.

The first peace talks in two years collapsed last week before they began in the face of the government offensive, one of the biggest and most consequential of the five-year war.

Thursday’s meeting in the German city of Munich was meant to allow powers to coordinate support for ongoing negotiations, but instead has turned into a desperate bid to ressurrect them.

A Western diplomat told Reuters that U.S. Secretary of State John Kerry wanted an immediate ceasefire in Syria – “All or nothing”. Moscow, however, had proposed a truce that would begin only from the start of next month, giving its Damascus allies 18 more days to recapture Aleppo, once Syria’s largest city.

Western powers were hopeful wording could be agreed that at the very least would allow more access for aid to besieged areas.

“Here we need something of a breakthrough,” said German Foreign Minister Frank-Walter Steinmeier. “Today, we will try what has not been achieved so far especially, to get better supplies to people locked in Syria and link this to first steps in a significant reduction of violence.”

But a senior Western diplomat summed up the pessimistic outlook: “This meeting risks being endless and I fear the results will be extremely small.”

Russia’s intervention on the battlefield on behalf of President Bashar al-Assad since last October has swung the momentum. The latest advance over the past two weeks has seen government forces and allies rout rebels and come close to encircling Aleppo, a divided city half held by rebels for years.

Russia’s Foreign Minister Sergei Lavrov, who met Kerry ahead of the talks, said Moscow had submitted proposals for a ceasefire and was awaiting a response from other powers. But Western officials do not expect Moscow to accept the immediate halt to bombing Washington seeks.

Kerry said he expected a “serious conversation”.

“Obviously, at some point in time, we want to make progress on the issues of humanitarian access and ceasefire,” Kerry said.

Russia is widely viewed as unlikely to halt support for the government advance until Damascus achieves its two main objectives: recapturing Aleppo and sealing the Turkish border, for years the lifeline for rebel-held areas.

That would amount to the most decisive victory of the war so far, and probably put an end to rebel hopes of removing Assad by force, their goal throughout five years of fighting that has killed 250,000 people and driven 11 million from their homes.

“The goal is to totally liberate Aleppo and then to seal the northern border with Turkey,” said Ivan Konovalov, director of the Center for Strategic Trend Studies in Moscow, explaining the Russian government thinking. “The offensive should not be stopped – that would be tantamount to defeat.”

“RISKS BEING ENDLESS”

Washington is leading its own air campaign against Islamic State militants in eastern Syria and northern Iraq, but has resisted calls to intervene in the main battlefields of Syria’s civil war in the west of the country, where the government is mostly fighting against other insurgent groups.

That has left the field to the Russians, who support Assad against an array of rebel groups backed by Turkey, Arab states and the West.

U.S. Defense Secretary Ash Carter drew a distinction between the two main zones of the conflict, saying Islamic State would have to be defeated “whatever happens with the Syrian civil war”.

In further evidence of the complexity of a multi-sided civil war that has drawn in regional and global powers, Russia provided air support for Kurdish fighters who overran a military air base that had been in the hands of Syrian rebels since 2013.

The Syrian Kurds have worked with the United States against Islamic State, but are opposed by Turkey, Washington’s NATO ally. The Kurds now appear to be taking advantage of the government advance to expand territory by capturing the Menagh base near the Turkish border.

One rebel commander, Zekeriya Karsli from the Levant Front, said: “The fall of Menagh airport has made the situation on the ground pretty grim.”

Saudi Arabia, which backs some of the rebels that Moscow is helping to defeat, has floated the idea of sending ground troops to help the U.S. effort against Islamic State. This was criticised by Russia’s Prime Minister Dmitry Medvedev, who said it could make the war permanent.

“All sides must be compelled to sit at the negotiating table instead of unleashing a new world war,” he told Germany’s Handelsblatt newspaper.

RUSSIANS AS MEDIATORS

Syria’s national reconciliation minister, Ali Haidar, suggested Moscow was playing a bigger role on the ground than just offering air strikes and military aid: Russian mediators were helping the government broker local deals with rebels willing to lay down weapons or relocate.

“The truth is that since the presence of the Russians on Syrian land, they can play the role of mediator in some areas,” Haidar told Reuters at his offices in Damascus.

The Russian-backed government assault has sent tens of thousands of people fleeing towards the Turkish border. The United Nations has said it fears for 300,000 people still trapped in Aleppo.

In a speech, President Tayyip Erdogan said Turkey’s patience may run out and Ankara may have to take action, but gave no details of what he meant. Erdogan called on the United Nations to prevent “ethnic cleansing”, saying as many as 600,000 more refugees could arrive.

The refugee crisis has had far-reaching impact across Europe, where Syrian refugees were the bulk of the biggest wave of migrants since World War Two to reach the European Union.

The NATO alliance announced a new sea mission to help Turkey and Greece crack down on criminal networks smuggling refugees from Turkey into Europe, after thousands drowned and hundreds of thousands made the journey last year.

Turkey has already taken in 2.6 million Syrians, the largest refugee population on earth, and has agreed to help keep them from travelling into Europe in return for aid. Erdogan warned that Turkey could “open the gates” for refugees into Europe if it did not receive enough help.

The United Nations and the European Union, which has agreed a 3-billion-euro fund to improve conditions for refugees in Turkey, have both urged Ankara to admit those fleeing the latest fighting.

“They struck Aleppo so we fled. First we escaped to another village. We’ve gone to every village. But they’re bombing everywhere so we came here,” said Musa Ibrahim Isa, one of the tens of thousands of people at Bab al-Salama, on the Syrian side of the border.

“Our only wish from God is that these gates be opened.”

(Additional reporting by Shadia Nasralla and Denis Dyomkin; Writing by Giles Elgood and Peter Graff; Editing by Peter Millership and Andrew Heavens)