According to the deal, military action, including airstrikes conducted by Syria, Russia and the US-led coalition will continue against Daesh, al-Nusra Front, as well as other UN-designated terrorist groups.
"Several FSA brigades announced of the refusal to join the ceasefire in Syria, if it does not apply to the Nusra Front," the commander was quoted as saying by Al Mayadeen television channel.
"There will be no ceasefire without Nusra Front," the commander said.
On Monday, the Kremlin released details of the Syrian ceasefire plan the US and Russia agreed upon. The two countries had to conduct several rounds of secret negotiations before settling all details and making them public. According to Russian President Vladimir Putin, the plan of ceasing hostilities presents a "real step that can stop the bloodshed."