There are reports of fierce fighting and clashes after foreign-backed militants try to enter an eastern suburb of the Syrian capital in violation of a nationwide ceasefire.
Anti-government sources and state media are reporting clashes between troops and armed groups as well as shelling in two neighborhoods of Damascus.
Syrian state news agency SANA said Friday militants shelled government-held areas in the eastern neighborhood of Qaboun, wounding three people.
The so-called Syrian Observatory for Human Rights, based in London, said Friday's fighting is concentrated in the neighborhood of Jobar, next to Qaboun.
According to the French news agency AFP, the Syrian army is blocking an attack by armed groups that tried to enter the capital's east via Jobar.
A barrage of rocket fire and shelling could be heard coming from the Jobar district which is held by militants, it said.
The offensive comes after the Russian Defense Ministry said it had recorded dozens of violations of the ceasefire agreement. Moscow also said units of militants "controlled by the US" have intensified their shelling of civilian residential areas.
On Thursday, Russia said the United States was using "a verbal smokescreen" to hide its reluctance to fulfill its part of the ceasefire agreement.
The Foreign Ministry said Russian and Syrian forces had stopped bombing areas held by militants but the US was complicating efforts to fight terrorists by not providing the exact locations of what Washington regards as "moderate" groups.
After the fourth day of the ceasefire, only Syria's government forces are observing the truce, the Russian ministry said in a statement.
US State Department spokesman Mark Toner said that "despite sporadic reports of violence, the arrangement is holding and violence is significantly lower."
The ceasefire was brokered to enable essential aid to get through to Syrians who are in desperate need of food stuffs and medical supplies.
On Friday, an anti-government "activist" said Russian troops have deployed along a main road leading into besieged militant-held neighborhoods of the northern city of Aleppo ahead of the possible arrival of aid convoys.
The arrangement came as 20 lorries, allegedly loaded with food and medical aid, waited at the Turkish border to be given the all clear to head to Aleppo.
The Russian Defense Ministry had said Thursday that the Syrian army was ready to bring back troops from the Castello Road, which leads into Aleppo, to ensure the safe movement of the convoys.
Rami Abdurrahman of the so-called Syrian Observatory for Human Rights said the Syrian government forces that were stationed there have been replaced by Russian troops. He said aid is expected to enter militant-held Aleppo later Friday.
