Syria's main umbrella of opposition and rebel groups said Friday that dozens of factions had agreed to abide by the cease-fire due to go into effect at midnight.

The alliance, known as the High Negotiations Committee, said in a statement that 97 factions would respect by the truce. It added that it has formed a military committee to follow up on the cease-fire.

Russia and the United States brokered the cease-fire, which does not include the Islamic State of Iraq and Syria (ISIS) or the Nusra Front, al-Qaeda's branch in Syria.

The Syrian government has said it will abide by the truce but will have the right to retaliate for any attacks. The opposition has demanded that Russia and Iran, President Bashar Assad's main backers, also abide by the truce.

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CBS News correspondent Elizabeth Palmer, reporting from near the front line in the war south of Damascus, said Friday that Turkey had also weighed in with a caveat; reserving the right to continue fighting Kurdish groups based along its southern border.

While Turkey considers the Kurdish separatists terrorists, they have been a crucial force in the fight against ISIS in the north of Syria.

Palmer reported that, in the hours leading up to the truce taking effect, the fighting only seemed to get more intense.

Driving down into the south of Syria from Damascus, she and her crew heard the sounds of rocketing and bombing constantly.

The British-based Syrian Observatory for Human Rights said Bashar Assad's army -- with its vital Russian backing -- remained on aggressive attack.

A spokesman for Turkish President Recep Tayyip Erdogan told reporters Friday that Turkey supports the cease-fire agreement in principle but is worried about the continued operations by Russia and Syria.

He said the "fact that Russian bombings and attacks by Assad's forces continued even last night, is leading to serious concerns on the future of the cease-fire."

Excluding the designated terrorist groups and all the exceptions to the truce maintained by the primary parties to the conflict, the United Nations is hoping there are enough smaller opposition groups on board to quell the violence enough so that aid and supplies can at least reach the hundreds of thousands of desperate people who have been cut off for months, or even years.