After the third day of the ceasefire, only Syria's government forces are observing the truce, the ministry said in a statement, Reuters reported.
It said that units of the opposition "controlled by the US" have intensified their shelling of civilian residential areas.
The truce brokered by Russia and the United States began at sundown Monday, in the latest bid to end a conflict that has killed more than 400,000 people since March 2011.
The agreement aims to bring an end to fighting between Syrian President Bashar Assad's forces and a wide range of foreign-backed militants but excludes terrorists groups like Daesh (ISIL).