US Secretary of State John Kerry said on Friday that there is an "urgent need" for the regime of Bashar al Assad to stop violating a cessation of hostilities agreement in Syria and called on Russia to put pressure Assad, the State Department said.
"The United States expected Russia to urge the regime to comply with the cessation and that we would work with the opposition to do the same," Kerry said in a telephone call with his Russian counterpart Sergey Lavrov.
Kerry's call came as a new round of fierce fighting around the northern city of Aleppo overshadowed peace talks aimed at ending Syria's six-year civil war.
State Department Spokesman John Kirby said at a news briefing that the US knows that some of the Syrian regime actions in and around the city of Aleppo are being backed by Russian air strikes.
Kirby said Kerry told Lavrov that the US was concerned about credible reports of violation in and around Aleppo "and to the degree that they are aided and abetted by Russian air strikes - yes that's a matter of concern for us."
As Kerry is urging Russia to press the Assad regime to stop the violations, he "promised that we would do the same on our part for the opposition groups that we are supporting," Kirby added.
US officials have complained that Russian warplanes appear to be flying in support of the regime forces attacking opposition areas in Aleppo, Syria's second city, despite Moscow having signed on to efforts to promote a political settlement.
However, the situation has been complicated by the presence of militants from the Syria-based Al Qaeda-affiliated group Nusra Front in Aleppo.The group is not party to the ceasefire and both Moscow and Damascus reserve the right to strike groups they regard as terrorists.
Besides, Kerry also protested to Lavrov about an incident this week in which Russian fighter jets repeatedly buzzed a US naval vessel in the Baltic Sea. And he urged Moscow to prevent ceasefire violations along the frontline in divided Ukraine.