It said there was no news on casualties.
Government forces repelled the attack and secured the road.
The Syrian opposition appears at odds with its Western backers over the success of the truce.
Since the failure of a first round of peace talks in 2014, the main sticking point in the negotiations has been the fate of Assad.
The threat of the ceasefire ending hangs over planned peace talks which are set to begin on March 10.
Assad, his war effort buoyed by five months of Russian air strikes, has said the army is respecting the agreement.
The partial truce, drawn up by Washington and Moscow, came into force on February 27th, and it has slowed the pace of the war, but it does not include Islamic State militants or the al Qaeda-linked Nusra Front.
At least 135 people have been killed since the ceasefire started but it has enabled many civilians to receive badly needed aid.
There have also been "mobilizations to occupy very important strategic areas", he went on to claim.
The head of another rebel group, who asked not to be identified for security reasons, said 40 army vehicles loaded with weaponry were seen heading northwards on Thursday night.
"Despite the drop in military operations in the field, there has been a pickup in hostilities from the Syrian regime and its allies, including Russia", Makhos said.
"Lorries are waiting for 36 hours", de Mistura told the pan-Arab newspaper Al-Hayat. Millions more have been forced from their homes.
Mr de Mistura attempted to convene peace talks in January, but these failed before they had even started in earnest.
"Assad has to leave at the beginning of the process", Saudi Foreign Minister Adel al-Jubeir told reporters in Paris.
De Mistura said he plans to invite members of the government, the opposition, civil society and women to the peace talks.
David Cameron took part in a conference call about the truce with the leaders of Russia, Germany, France and Italy on Friday. Russian Federation has stood by him. Warplanes struck a key rebel bastion east of the Syrian capital for the first time since the fragile truce began last weekend, a monitor said.
Asked how Putin had responded, the spokeswoman said there was no detailed discussion on the Syrian president. Also 25 Syrian soldiers were killed as well as 27 fighters with the Syrian Kurdish Forces.
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