Talks aimed at securing peace in Syria were suspended Wednesday as President Bashar al-Assad's regime secured a major battlefield victory against rebels and his ally Russia vowed no-let up in air strikes.
The United States and France condemned the Russian bombing around Syria's second city of Aleppo, with French Foreign Minister Laurent Fabius accusing the government and its backers of "torpedoing the peace efforts".
After failing over several days to get peace negotiations off the ground in Geneva, UN special envoy Staffan de Mistura announced a suspension of the talks.
"I have indicated from the first day I won't talk for the sake of talking," he told reporters.
"I therefore have taken the decision to bring a temporary pause (until February 25). It is not the end or the failure of the talks," he added, saying "more work" was needed, including from outside powers embroiled in the complex conflict.
Backed by external powers embroiled in Syria's war, the negotiations are seeking to end a conflict that has killed more than 260,000 people and fuelled the meteoric rise of the extremist Islamic State group.
But the main opposition umbrella group, the High Negotiations Committee (HNC), said it would not return to Geneva until its the regime alleviates the dire humanitarian situation on the ground in Syria.
The UN announcement came as Syrian troops, helped by days of Russian air sorties, cut the last supply route linking rebels in Aleppo to the Turkish border.
Syria's pre-war commercial capital has been divided between loyalists in the west and rebels in the east since fighting erupted in the northern city in mid-2012.
Assad's forces, aided by Lebanon's Iranian-backed Hezbollah and other militias, encircled Aleppo from the west, south and east, and have advanced from the north since last week.
- Supply route cut -
On Wednesday, the army broke a three-year rebel siege of two government-held villages and took control of parts of the supply route, a Syrian military source told AFP.
The offensive is one of several the government has launched since Russia threw its military might behind Assad, adding to support from Iran, on September 30.
Russian Foreign Minister Sergei Lavrov said Wednesday he saw no reason for the air strikes to stop until the "terrorists" are defeated.
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"The regime forces have done in three days in Aleppo what they had failed to do in three years, thanks mainly to Russian support," said Rami Abdel Rahman of Britain-based monitoring group the Syrian Observatory for Human Rights.
Since the conflict began in March 2011, more than half of Syria's population have fled their homes, many of them heading to Europe. The UN said last month some 487,000 people were living under siege, among 4.6 million people in so-called "hard-to-reach" areas.
De Mistura's brief is to coax both sides into six months of indirect "proximity talks" envisioned under a November roadmap proposed by outside powers, but problems beset the Geneva gathering from the outset.
The HNC arrived several days late, and reluctantly, insisting on immediate steps to allow aid to get through to besieged cities, a halt to the bombardment of civilians and the release of thousands prisoners.
Riad Hijab, HNC chief coordinator, said late Wednesday the group "will not return until the humanitarian demands are met or (we) see something on the ground".
"The whole world sees who is making the negotiations fail, who is bombing civilians and starving people to death," Hijab told reporters, adding the Russian-backed advances showed the government was not genuinely interested in peace talks.
- 'Asphyxiate Aleppo' -
The US State Department said the Russian air strikes were harming attempts to secure peace.
"It is difficult in the extreme to see how strikes against civilian targets contribute in any way to the peace process now being explored," said State Department spokesman John Kirby.
France's Fabius in a statement condemned "the brutal offensive by the Syrian regime, with the support of Russia, to encircle and asphyxiate Aleppo".
He said France supported de Mistura's decision to halt the talks to which neither "Assad's regime nor its supporters apparently want to contribute in good faith, thereby torpedoing the peace efforts".
World leaders will take stock of the suspended Geneva talks when they gather in London on Thursday for a donor conference to help Syrians and neighbouring countries affected by the crisis.
The Syrian government delegation in Geneva, meanwhile, complained that the Saudi-backed HNC was disorganised, had not named its negotiators and contained individuals it considered "terrorists".
One such figure is Mohammed Alloush, a leading member of Islamist rebel group the Army of Islam and nominally the HNC's chief negotiator, who arrived in Geneva late on Monday.
Bashar al-Jaafari, chief government negotiator, blamed the suspension on opposition "preconditions" and said de Mistura announced the break only because the HNC was about to leave.