In a phone call on Monday, Kerry told his Russian counterpart, Sergei Lavrov, that Moscow has “special responsibility” over the strikes Washington blames on the government of Bashar al-Assad.

Kerry made those accusations while the airstrikes by the US and its allies, purportedly against ISIS, have led to civilian causalities, targeted the country's infrastructure in many instances and have done little to stop the advances of terrorists.

"Russia has a special responsibility in this regard to press the regime to end its offensive attacks and strikes that kill civilians, immediately allow relief supplies, as determined solely by the UN, to reach all in need, and to comply completely with the cessation of hostilities," State Department spokesman Mark Toner said.

Toner also noted that the US government has no intention to launch joint military operations with Russia in Syria.

"We're not looking at joint operations," said Toner. "We're discussing with them proposals for sustainable mechanisms to better monitor and enforce the cessation of hostilities - we're not talking about joint operations."

On Friday, Russian Defense Minister Sergei Shoigu said that Washington and Moscow should carry out joint airstrikes against the Takfir Nusra Front and other terrorist groups that do not support the truce reached by Moscow and Washington to facilitate negotiations between warring sides to the conflict.

Shoigu also called for joint strikes to be conducted against "convoys containing weapons and ammunition, armed units that illegally cross the Syrian-Turkish border."

However, Pentagon spokesman Navy Captain Jeff Davis rejected the appeal later that day, saying, "We do not collaborate or coordinate with the Russians on any operations in Syria."

The Syria truce, which went into effect late February, is still officially in place in many parts of Syria despite surging violence in Aleppo.

Syria has been gripped by militancy since March 2011. Damascus has long been saying that Saudi Arabia, Turkey and Qatar are funding and arming anti-Syria terrorist groups, including ISIS terrorists.

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