Russia has accused U.S.-backed rebel groups of having repeatedly violated the latest cease-fire in Syria and urged the United States to pressure violators into compliance.
Senior Russian military officer Viktor Poznikhir said on September 13 that government troops "stopped all fire everywhere," except for areas where the Islamic State and Jabhat Fateh al-Sham extremist groups operate.
"Regrettably, the same cannot be said about armed groups of the U.S.-controlled moderate opposition," Poznikhir added. "After the start of the cessation of hostilities by this morning 23 instances of firing on residential areas and government positions were registered."
"We strongly call on all those who have influence on these cease-fire violators, first and foremost the American side, to finally deal with their clients," Russia's Foreign Ministry later said. "One should not allow their expected provocative actions to derail a chance for a turn to a political resolution of the Syrian crisis."
Meanwhile, the United Nations envoy for Syria has applauded the "significant drop in violence" in the 24 hours since a cessation of hostilities came into effect.
"The situation has dramatically improved", Staffan de Mistura said on September 13, adding that, if the truce held, aid deliveries to besieged Syrians "should be taking place very, very soon."
Syrian activists have reported sporadic violence carried out by both government and rebel forces since the truce came into force at sunset on September 12.
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.
The truce 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.