It is the ISSG's first full meeting since the talks on a political transition in Syria collapsed, partly because of opposition protests against Russian-backed operations in Aleppo.
Syria support group 'discussing Russian peace plan' in Munich
The 17-nation group of major powers, which includes Damascus-backers Russia and Iran, is meeting on the sidelines of the Munich Security Conference.
On Tuesday, US Secretary of State John Kerry urged Russia to join efforts to bring about a ceasefire.
"Russia's activities from Aleppo and in the region are making it much more difficult to be able to come to the table and be able to have a serious conversation," Kerry told reporters.
Despite pessimism in some circles, Kerry said the United States and other world powers were approaching the talks in Munich with "great hopes".
"Russia needs to join all of us in understanding that this can not go on," said Kerry. "They have a major responsibility as a co-convener of the International Syria Support Group to create the framework within which that group can be successful."
But in comments published on Tuesday, the Russian foreign minister shrugged off criticism that his country had contributed to the collapse of peace talks in Geneva last week by providing air cover for the Syrian government advance north of Aleppo.
Sergei Lavrov also said Moscow had now presented Washington with new proposals for ending the war.
Lavrov is set to meet with US Secretary of State John Kerry on the sidelines of the conference.
The resumption of peace talks face many obstacles, led by bickering over Russia's role and the fate of Bashar al-Assad in the transition in Syria |
Assad regime forces and allied militias have now all but encircled rebel-held parts of the Aleppo and its countryside, causing tens of thousands to flee in the direction of the Turkish border, and raising concerns of a major humanitarian crisis for hundreds of thousands trapped in the city.
More than 500 people, including dozens of civilians, have been killed since the major Russian-backed government offensive in Syria's Aleppo province began this month, according to activists.
The Syrian Observatory for Human Rights said on Wednesday the toll of 506 included 23 children killed in Russian airstrikes on Aleppo city and its surroundings since the operation was launched on Feb. 1.
Ahead of the Munich meeting, the UN Security Council will discuss the humanitarian situation in Syria and the recent displacement of tens of thousands of people.
The closed-door consultations are scheduled on Wednesday and were jointly requested by New Zealand and Spain, backed by other Western powers.
"There are reports of at least 30,000 people displaced from Aleppo and it's the middle of winter," New Zealand Ambassador Gerard van Bohemen said in a statement to Reuters. "New Zealand and Spain considered this was a situation the Security Council could not ignore."