Russia pressed on with its bombing campaign in support of Syrian President Bashar al-Assad on February 12 despite agreeing to a pause in combat in Munich negotiations.
Russian bombs killed 16 civilians in Syria hours after world powers agreed to cease hostilities within a week, Turkish Foreign Minister Mevlut Cavusoglu told world leaders gathered in Munich.
He joined a chorus of western leaders and NATO allies calling on Russia to stop.
"What is important now is embracing this opportunity, stopping the air strikes, ceasing targeting civilians, and providing humanitarian access," Cavusoglu said later on Twitter.
Western leaders have said there is no hope for progress in Syrian peace talks without a halt to the Russian bombing, which in recent weeks has helped turned the ground war in favor of Assad.
"Through its military action on the side of Assad's regime, Russia had recently seriously compromised the political process. Now there is a chance to save this process," German Foreign Ministry spokeswoman Christiane Wirzt said.
But Russia and Syria have continued to insist that the opponents they are fighting in Aleppo, including those backed by Turkey and Saudi Arabia, are "terrorists" and thus their campaign can proceed under the truce agreement, which exempts fighting against recognized terrorist groups.
In an interview with AFP released on February 12, Assad asserted that all opposition groups that have taken up arms against the government are "terrorists," and thus his forces can continue to fight them during peace negotiations.
Even if Russia and Syria agreed to stop fighting in Aleppo in a week's time, by some estimates the additional week of fighting would give them enough time to encircle what was Syria's biggest city before the war, and possibly even capture it.
Moreover, they are also close to sealing theTurkish border north of Aleppo, where deliveries of supplies have provided a lifeline for rebels, and they might be able to accomplish that task before honoring the truce.
While western powers agreed to exempt air raids on Islamic State (IS) and Al Nusra Front, Al-Qaeda's Syrian affliate, from the truce, they have insisted that other rebel groups fighting Assad -- many of them participating in the peace negotiations -- are covered.
White House spokesman Eric Schultz said on February 12 that Russian air raids have been targeting areas where there is no IS presence, although the Nusra group is active in Aleppo and has ties to other rebel groups there.
"It is time for [Russia] to stop using the cover of going after ISIL," Schultz said.
The United States raised the threat of escalation in the ground war, apparently in a bid to force Russia and Syria to comply with the truce.
U.S. Secretary of State John Kerry, who is in Munich, warned that if the truce fails, more foreign troops could enter the conflict.
"If the Assad regime does not live up to its responsibilities and if the Iranians and the Russians do not hold Assad to the promises that they have made...then the international community obviously is not going to sit there like fools and watch this. There will be an increase of activity to put greater pressure on them," Kerry told Dubai-based Orient TV.
"There is a possibility there will be additional ground troops," Kerry said.
Saudi Arabia and Bahrain have both offered to deploy ground forces in Syria. Despite agreeing to the truce, the Saudis on February 12 said they remain prepared to send fighters and are just as determined as ever to end Assad's rule by whatever means necessary.
"There will be no Bashar al-Assad in the future," despite Russia's backing, Saudi Foreign Minister Adel al-Jubeir told the German newspaper Sueddeutsche Zeitung.
With reporting by Reuters, AP, and AFP