Russia has accused the United States of failing to meet its obligations under the Syria cease-fire agreement.
In a statement on September 15, Russian military spokesman Igor Konashenkov claimed Washington was using a "verbal curtain" to hide what he said was its reluctance to rein in the opposition groups it supports.
The cease-fire has largely held since taking effect on September 12, with only minor violations reported.
The cease-fire deal was brokered by Russia and the United States, which are backing different sides in Syria's five-year-old civil war.
The Kremlin supports President Bashar al-Assad, while the United States is backing rebel groups seeking his ouster.
If the cease-fire holds for a week, the United States and Russia are to carry out coordinated air strikes against Jabhat Fateh al-Sham, formerly the Al-Qaeda-linked Al-Nusra Front, and Islamic State militants.
The truce does not apply to these two extremist groups.