Russian military forces have said that rebel groups in Syria have stepped up their activities, despite a ceasefire agreement.
The ceasefire was brokered between Russia, which backs President Bashar al-Assad with air power, and the US, which supports some mainstream rebel groups. It came into effect at sunset on Monday (12 September) and has been working to ease fighting.
However, Russian General Vladimir Savchenko has said "the situation in Syria is worsening", with 55 attacks over the past 24 hours, leading to the deaths of 12 civilians.
General Viktor Poznikhir said the rebel groups had "not met a single obligation" of the truce.
"If the American side does not take the necessary measures to carry out its obligations… a breakdown of the ceasefire will be on the United States," he said. "The United States and the so-called moderate groups they control have not met a single obligation they assumed in the framework of the Geneva agreement."
The terms of the ceasefire require mainstream rebel groups to separate themselves from militant factions.
"Without separating, the government troops' hands are tied," Gen Poznikhir said. "Our repeated messages to the American side are left without a response. There is doubt that the US is able to influence the moderate opposition they control."
Russia's Defence Ministry said conditions in Syria were deteriorating, adding that it believed the ceasefire had been breached 199 times by rebels and saying the US would be responsible if it were to collapse.
Both sides have accused the other of delaying aid deliveries to Aleppo, where army and rebel forces were supposed to pull back from the Castello Road which leads into insurgent-held eastern districts.
Russia on Friday said the Syrian army had initially withdrawn but returned to its positions after being fired on by rebels, who in turn say they saw no sign of government forces ever leaving their positions.
"There is no change," said Zakariya Malahifji, an official for a rebel group in Aleppo on Saturday (17 September), when asked whether there had been any move by the army to withdraw from positions along the road.
The United Nations said the government was holding up aid by denying letters guaranteeing access. At least 20 trucks have been waiting since Monday for the credentials which would allow them safe passage from Turkey into Syria and on to east Aleppo.
Warplanes have been strafing or bombing rebel-held areas in the northwestern province of Idlib, as well as positions north of the city of Homs and east of the city of Hama overnight, according to the Syrian Observatory for Human Rights.
The war monitoring group also reported clashes between the army and rebels or shelling overnight in the capital's Eastern Ghouta suburbs, in Ramousah south of Aleppo and in the southern province of Deraa.
President Vladimir Putin said Moscow was keeping to its obligations under the truce, and the Syrian government was "fully abiding" by the agreement.
Speaking on television in Kyrgyzstan on Saturday (17 September), he said that the US seemed to be trying to maintain the rebels' military capability in its conflict with the government, adding that this was a "dangerous path".