World powers convening in Munich on Thursday are working towards a ceasefire to end hostilities in Syria's civil war, German Foreign Minister Frank-Walter Steinmeier said ahead of a meeting of the International Syria Support Group.
Negotiators are working towards "a marked reduction of violence and hopefully at the end an agreement on a ceasefire, but I cannot tell you at this point whether this will be possible tonight," Steinmeier said.
US Secretary of State John Kerry and his Russian counterpart Sergei Lavrov are meeting European and Middle Eastern foreign ministers on the eve of the Munich Security Conference to push for a breakthrough ahead of peace talks scheduled to resume in Geneva on February 26.
"We have put forward our proposals on a ceasefire, which are rather concrete," Lavrov said ahead of the talks, according to the Russian news agency Tass. "We are waiting for an answer from the US before offering them for consideration of the International Syria Support Group."
The US State Department did not confirm reports that Moscow had suggested March 1 as a potential start date for a ceasefire.
Speaking ahead of the talks in Munich, Riyad Hijab, the chief negotiator for the Syrian opposition, named several preconditions for a cessation of hostilities on the ground.
There will be a ceasefire when "there is a political transition, when [President] Bashar al-Assad is no longer in power, and when foreign troops and mercenaries have left" the country, he said.
The talks come against the backdrop of a significant military escalation in Syria as al-Assad, backed by Russian airstrikes, is advancing against rebels.
Syria's Kurdish fighters have seized a strategic airbase from Islamist rebels in the northern province of Aleppo, monitors said.
Fighters from the Kurdish People's Protection Unit (YPG) and Arab allies overran the Mingh military airport, strategically located between Aleppo city, the capital of the province, and the Kurdish-controlled northern town of A'zaz, the Syrian Observatory for Human Rights said.
Warplanes, believed to be Russian, carried out at least 30 airstrikes in support of the Kurds as they advanced in the area.
Rami Abdel-Rahman, head of the Observatory, described the Russian airstrikes as a sign of an "undeclared coordination" between the Kurds and Moscow, which launched its aerial campaign in Syria in September.
Rebel groups in Aleppo are grappling with two simultaneous attacks - one mounted by Kurdish forces from the west and another by the regime forces from the north.
Nearly 270,000 people – including more than 78,000 civilians - have been killed in the conflict that started in 2011, according to the Britain-based Observatory.
In Geneva, UN human rights chief Zeid Ra'ad Al Hussein slammed the various actors in the Syrian conflict for showing less and less regard for civilian lives.
"Women and children, the elderly, the wounded and sick, the people with disabilities are being used as bargaining chips and cannon fodder day after day, week after week, month after month," the UN high commissioner for human rights said.
The attacks on rebel-held Aleppo have forced some 51,000 civilians to flee, while putting 300,000 at risk of becoming trapped in a siege, Zeid said, adding that dozens of civilians have been killed and at least three clinics have been destroyed.
Dr Mahmoud Mustafa, who is working in camps in Bab al-Salameh, across the border from Turkey, told dpa that the number of people at the camps was growing because of the Russian strikes.