Columbia: US Secretary of State John Kerry called his Russian counterpart Foreign Minister Sergei Lavrov on Friday to demand that Moscow press its Syrian allies to respect a crumbling ceasefire.
"Secretary Kerry 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," US spokesman John Kirby said.
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 five-year civil war.
According to Kirby, Kerry told Lavrov of Washington`s "serious concerns over the ongoing threats to the cessation of hostilities in Syria and the urgent need for the Assad regime to stop its violations of the cessation."
US officials have complained that Russian warplanes appear to be flying in support of Syrian forces attacking rebel positions in Aleppo, Syria`s second city, despite Moscow having signed on to efforts to promote a political settlement.
But the situation has been complicated by the presence of fighters from the Al-Qaeda-linked Al-Nusra Front in Aleppo.
Nusra is not party to the ceasefire and both Moscow and Damascus reserve the right to strike groups they regard as terrorists.
On the call Kerry "made it clear that we`re concerned about the violence in and around Aleppo, and that we`re concerned about reports -- which we believe have credibility -- that there are violations of the cessation happening," said Kirby.
"And to the degree that they`re aided and abetted by Russian air strikes, yes, that`s a matter of concern for us."
The top US diplomat also expressed to Lavrov concern about reports that Iranian general Qassem Suleimani, commander of the covert wing of the Revolutionary Guards Corps, is visiting Moscow.
Suleimani leads the Quds Force, which trains and supports Shiite militias in Lebanon, Iraq and Syria. He is subject to a travel ban under United Nations sanctions targeting Iran`s guerrilla campaigns.
"He did raise it in the call," Kirby confirmed. "We`re aware of reports that General Suleimani has travelled to Russia. I`m not in a position to confirm whether that`s actually true.
"But as we`ve said when there have been previous reports of similar travel, there are UN sanctions on General Suleimani that remain in effect so such travel if true would be a violation of UN Security Council resolutions and we believe then a serious matter of concern both for the UN and for the United States."
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.