The UN Security Council has unanimously passed a vote to support a pause in fighting in Syria and demanded that all parties to the agreement fulfill their commitments to end hostilities.
The vote came less than an hour before the start of a proposed "cessation of hostilities", which began at midnight Damascus time on Saturday (22:00 GMT Friday).
The council on Friday adopted a resolution drafted by the US and Russia that endorses the ceasefire deal, with UN Syria envoy Staffan de Mistura saying Syrian peace talks will reconvene on March 7 if the ceasefire holds.
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"Assuming ... the cessation of hostilities largely holds, God willing, and the humanitarian access continue unabated, I intend to reconvene ... the intra-Syrian talks on Monday, March 7," de Mistura said.
Al Jazeera's diplomatic editor, James Bays, reporting from the UN headquarters in New York, said it would take some time to see if the conditional truce will hold.
"You can have a cessation of hostilities on paper...but right now is the crucial moment to see whether there will be a lull in fighting," he said, moments after the agreement came into effect.
Earlier on Friday, Syria's main opposition bloc said that almost 100 factions had agreed to respect a temporary truce, as air strikes by suspected Russian jets continued hitting rebel-held areas hours before the proposed ceasefire came into force.
The opposition alliance, known as the High Negotiations Committee (HNC), said in a statement that 97 factions and armed groups fighting the forces of President Bashar al-Assad would respect a two-week truce.
The HNC also demanded that Russia and Iran, Assad's main backers, also abide by the truce.
The Syrian government has previously said it would abide by the truce, but would have the right to retaliate for any attacks.
But later on Friday, Abu Mohammed al-Golani, the leader of al-Nusra Front, rejected the cessation of hostilities and called upon fighters to intensify attacks against Assad and his allies.
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In an audio message played on Orient News TV, Golani said that if Syria's war was not resolved, the consequences would spread to Sunni Muslims in other parts of the region, including the Arabian Peninsula.
"Fighters in Syria, willingly arm yourselves, intensify your attacks and have no fear of their troops and their aircraft," Golani added.
|Positions as of January 2016 [Al Jazeera]
Meanwhile, Russian President Vladimir Putin said on Friday that the peace process in Syria would be "complicated" but that there were no other ways of ending the conflict.
He added, however, that his country's air force would continue its bombing campaign against ISIL, al-Nusra Front and other "terrorist groups" in Syria after the truce deal enters into force.
"The decisive fight against them will, without doubt, be continued," the Russian president said during a meeting of the FSB security service in Moscow.
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Putin's comments came as the UK-based Syrian Observatory for Human Rights said that air strikes by suspected Russian warplanes were continuing to hit rebel-held positions on Friday hours before the deadline.
The rebel-held Damascus suburb of Douma was hit 40 times on Friday, the monitoring group said, along with other areas east of the capital, killing at least eight people, including three women and four children.
Mazen al-Shami, an activist based in the area, told the AFP news agency that the warplanes were Russian, adding that they carried out some 60 air raids on Friday. He said 25 strikes targeted Douma. "The air raids intensified after the revolutionary factions said they would abide by the ceasefire," al-Shami said via Skype.
Pact 'could end Syria's war'
On Thursday, US President Barack Obama said the proposed ceasefire could be a key step towards ending Syria's war.
Obama told a meeting of members of his National Security Council in Washington that halting air strikes was essential for the truce to be successful.
He added that ending fighting among various forces was the best route in tackling ISIL.
READ MORE: Syrian opposition accepts ceasefire for 'two weeks'
"The only way to deal with ISIL in a way that defeats them in a lasting way is to end the chaos in the civil war that has engulfed Syria," Obama said.
"That's how ISIL was able to thrive in the first place."
Obama noted, however, that it remained to be seen whether the "cessation of hostilities" would hold.
The deal marks the biggest diplomatic push yet to end Syria's nearly five-year-old war which has killed more than 260,000 people and displaced millions from their homes.
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Source: Al Jazeera