GENEVA/MUSCAT - The United Nations strained to keep faltering Syrian peace talks alive on Wednesday as Damascus tried to press home gains against rebels and its ally Russia said its air strikes would go on until "terrorists" were defeated.
UN envoy Staffan de Mistura announced the formal start on Monday of the first attempt in two years to negotiate an end to a war that has killed 250,000 people, caused a refugee crisis in the region and Europe and empowered Islamic State militants.
But both opposition and government representatives have since said talks have not in fact begun, and fighting on the ground has raged on without constraint.
De Mistura acknowledged on Tuesday that a collapse of the Geneva talks was always possible.
"If there is a failure this time after we tried twice at conferences in Geneva, for Syria there will be no more hope. We must absolutely try to ensure that there is no failure," he told Swiss television RTS.
The opposition cancelled a meeting with him on Tuesday afternoon, accusing Russia of putting the process at risk with an "unprecedented" bombing campaign on Aleppo and Homs.
Rebels described the ongoing assault north of Aleppo as the most intense yet. One commander said opposition-held areas of the divided city were at risk of being encircled entirely by the government and allied militia, and appealed to foreign states that back the rebels to send more weapons.
"How can you accept to enter a negotiations when you have unprecedented military pressure? The Russians and regime want to push the opposition out of Geneva so the opposition bears the responsibility for the failure," said a senior Western diplomat.
Despite calls from the US and its allies for Moscow to stop the bombing during the peace process, Russian Foreign Minister Sergei Lavrov said his country had no intention of ending its campaign.
"Russian strikes will not cease until we really defeat terrorist organisations like Jabhat al-Nusra. And I don't see why these air strikes should be stopped," he said at a news conference in Oman's capital Muscat.
Diplomats and opposition members said they were also taken by surprise when de Mistura called for immediate efforts to begin ceasefire negotiations despite there being no official talks or goodwill measures from the Syrian government.
The opposition has said it will not negotiate unless the government stops bombarding civilian areas, lifts blockades on besieged towns and releases detainees.
"The level of confidence between both sides is close to zero," de Mistura told the BBC late on Tuesday.
"A ceasefire for me is essential. In fact it is the test that shows the talks are successful," he said, urging Russia and the United States to work with other major powers to bring it about.
The opposition tentatively said it would resume meetings with de Mistura on Wednesday. Its chief coordinator Riad Hijab, who diplomats say is a unifying figure for the fragmented opposition, is expected to arrive in Geneva later in the day.
De Mistura called on Monday for the International Syria Support Group, which brings together major powers who back and oppose Syrian President Bashar al-Assad, to tackle the issue of ceasefires immediately. The group is scheduled to meet in Munich on Feb. 11.
Opposition delegate Nazir Hakim said a general ceasefire in the current climate was "unrealistic".
"Regarding a ceasefire, we have pragmatic ideas and we talked with the Americans who head the Syria support group and we look forward to discussing these ideas at the meeting on February 11," Lavrov said.
The attack north of Aleppo that began in recent days is the first major government offensive there since Russian air strikes began on Sept. 30.
The area safeguards a rebel supply route from Turkey into opposition-held parts of the city and stands between government-held parts of western Aleppo and the Shi'ite villages of Nubul and al-Zahraa, which are loyal to Damascus.
The Syrian Observatory for Human Rights, which monitors the violence in the country, said Russian and Syrian war planes carried out dozens of air strikes against the rebel towns of Hayan and Hreitan in northern Aleppo on Wednesday.
A pro-government source in the area said that the army and its allies were around two km from Nubul and Zahraa, which have been under rebel siege for around three years.
Senior Syrian opposition negotiator Mohamed Alloush, representing Jaish al-Islam (Islam Army), a major rebel group, said he was not optimistic given the events on the ground.
"Our answer will come in two days," he told Reuters without elaborating.