Russian fighter jets carried out airstrikes against rebel-held areas in northwestern Syria on Thursday while regime forces bombarded the Damascus suburb of Daraya only a day before the proposed ceasefire is due to take effect.
Airstrikes focused on areas in Latakia province close to the Turkish where a number of rebel group including the al-Qaeda affiliate, al-Nusra Front holds ground.
Meanwhile, the Syrian Observatory for Human Rights said regime helicopters dropped at least 30 barrel-bombs on Daraya on Thursday.
The fighting comes only a day ahead of the proposed "cessation of hostilities" proposed through a US-Russian agreement that is due to take effect at midnight on Friday.
Also on Thursday, regime troops retook a strategic town of Khanasser from the Islamic State group (IS), paving the way for the reopening of its sole supply route to main northern city Aleppo.
The Observatory said troops still needed to clear militants from hills overlooking the key highway before it could be fully secured.
The road through the town of Khanasser is the sole link between government-held areas in and around Aleppo and those in the rest of the country.
State news agency SANA hailed its recapture just two days after its fall to the IS.
With the ceasefire deadline fast approaching, Syrian sources said that al-Nusra, who along with IS are excluded from the deal, vacated its positions in Idlib province north of Syria.
"Al-Nusra on Thursday vacated its bases and checkpoints in the city of Sarmada and the surrounding areas," local activist Abu Yasser al-Jabali told The New Arab.
The move by al-Nusra is believed to be precautionary measure as they anticipate their positions to be heavily bombarded Russian and coalition fighter jets starting Saturday, according to al-Jabali.
Syrian rebels have expressed their concern that the ceasefire will be used by Russia and the Syrian regime to strike against the opposition under the excuse of fighting al-Nusra and IS.
The ceasefire deal aims to pave the way for a resumption of UN-led Geneva peace talks that collapsed earlier this month.