U.S. Secretary of State John Kerry said Saturday that Russia's attacks in Syria have been largely "against legitimate opposition groups."
It's critical for Russia to stop attacking groups that should be part of peace talks, he said.
The International Syria Support Group, including Russia, "has agreed to work to make that happen," Kerry said. "There is no way to adequately deal with the cessation of hostilities unless we do sit down and work together on every aspect of this."
Groups getting bombed will be disinclined to talk, Kerry told the Munich Security Conference on Saturday.
Major world powers agreed this week to a "cessation of hostilities"
in Syria and delivery of immediate aid. But Kerry said much work remained to be done before peace would become a reality.
The civil war in Syria has raged for five years, destroying cities, killing nearly a half-million people and sending refugees fleeing to Europe.
Russia denies air attacks
For its part, Russia denied Saturday that it is bombing civilians in Syria, insisting instead that it is protecting itself from militants.
"There is no evidence of our bombarding civilians even though everyone is accusing us," Prime Minister Dmitry Medvedev told the conference.
Medvedev defended Russia's military action in Syria, saying it was aimed at protecting national interests and quashing militants.
His comments came after his French counterpart, Manuel Valls, warned Moscow that it is undermining peace in Syria.
"We need to have peace, we need to have negotiations, and for that, we need to stop bombings against civilians," Valls said during his speech in Munich.
Russia has carried out airstrikes in support of Syrian government forces battling for Aleppo.
War of words
As battles rage around the embattled Syrian city, so too has the war of words between Russia and the United States.
Russia's defense ministry turned the tables Thursday with accusations that the U.S. dropped bombs on Aleppo on Wednesday.
This back-and-forth over Syria among outside powers is hardly new. While they claim to have the same military mission -- to combat terrorists, specifically ISIS -- Moscow has been at odds with others over tactics and targets.
U.S.,Russia discuss Syria
The United States and its allies have characterized Russia as a major part of the problem in Aleppo, blaming it for cutting off the city from desperately needed food and aid.
Kerry met Saturday with Russian Foreign Minister Sergey Lavrov at the Munich conference to discuss Syria.
"During a brief discussion, the two ministers went over plans for the organization and essential tasks of the task force charged to develop modalities for a cessation of hostilities in Syria," U.S. State Department spokesman John Kirby said.
"They also briefly discussed the establishment and organization of the U.N. task force to coordinate humanitarian aid and initial steps taken by the U.N. to prepare for that delivery in coming days."
Both agreed aid should flow rapidly to communities the U.N. has said are most in need, such as Deir Ezzor and Madaya