The Russian military said it would not fly sorties across Syria on Saturday in order to avoid "bombing mistakes," as an internationally backed truce largely held since going into effect at midnight.

There were reports of regime artillery fire in certain pockets and a suicide bomb near Hama, where fighting has been intense between regime forces and "Islamic State" (IS). In Kurdish-controlled Tal Abyad, near the border with Turkey, there were reports of fighting between the Syrian Kurdish YPG and IS.

Activists, rebels and civilians reported relative calm across large parts of Damascus and central and northern Syria, where bombing and fighting has been the norm for years.

The truce, the result of months of diplomacy led by Russia and the United States, calls for a cessation of hostilities between warring parties and the delivery of humanitarian aid to civilians, paving the way for peace talks between the Syrian opposition and regime representatives.

Holes in the truce

At a late-night press conference in Geneva Friday, UN Syria envoy Staffan de Mistura said he anticipated breaches of the agreement but called for parties to show restraint and avoid escalations.

"Let's pray that this works because frankly this is the best opportunity we can imagine the Syrian people have had for the last five years in order to see something better and hopefully something related to peace," de Mistura said, adding that, if the truce holds, peace talks could begin on March 7.

There are many holes in the agreement, and doubts linger over how long the guns and bombs would remain silent.

The truce does not apply to IS and al Nusra Front, both internationally recognized terrorist organizations that Russia and the Syrian government have pledge to continue to pound.

Some rebel groups have voiced concern Russia and the regime could use the exclusion of al Nusra from the truce as an excuse to continue bombing opposition factions.

Al Nusra fighters are scattered across Idlib and Aleppo and have cooperated with various rebel groups. On Friday, the terror group urged rebels to increase attacks on Assad and his allies.

In a sign of how difficult it may be to halt the fighting, Ahrar al Sham, one of the biggest Islamist rebel factions in the north, appears not to have signed onto the ceasefire and instead vowed to continue cooperation with al Nusra.

This would potentially open up Ahrar al Sham, which the Syrian government has long argued is a terrorist group, to Russian bombing and regime advances in Idlib and Aleppo. Several rebel factions, in turn, have ties with Ahrar al-Sham.

US-Russia information exchange

Lieutenant General Sergei Rudskoi of Russia's General Staff said 17 armed groups - amounting to 6,000 fighters from the opposition or tied to the regime - had told Russia that they would adhere to the ceasefire.

He added that the US had also provided Russia with separate information on rebel groups that have told the US that they would take part. The two sides also shared maps designating areas that should fall under the ceasefire.

Under the truce terms agreed upon by the US and Russia, the co-chairs of the 17-member group of nations seeking to end the conflict, rebel factions and government militia must notify Russia or the US either directly or through representatives of their intent to abide by the terms of the ceasefire.

Syria's main opposition grouping, the High Negotiations Committee (HNC), said Friday that 97 opposition factions had agreed "to respect a temporary truce" - but only for an initial two-week period.

cw/rc (AFP, AP, Reuters)