A partial ceasefire in Syria's civil war appeared to be broadly holding Saturday, despite a number of reported breaches and a major offensive by Islamic State jihadists against Kurdish forces.
"Despite violations in some areas, I can say the ceasefire situation is good so far," Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, which has been documenting violence since the war in Syria started in 2011.
Abdel-Rahman said that most of the "grave violence" taking place on Saturday was in areas where the ceasefire did not apply.
Islamic State and Syrian al-Qaeda affiliate the al-Nusra Front are not part of the ceasefire because they have been designated terrorist organizations by the United Nations. That means that attacks upon them would be allowed under the terms.
However, Russia said it halted its air campaign in Syria on Saturday, taking into account the start of the ceasefire and in order to avoid mistakes.
The Russian Defence Ministry said the US had sent a list of 6,111 fighters who had signed up to the "cessation of hostilities" deal that went into effect at 2200 GMT Friday, and of 74 areas that should not be bombed.
Moscow and Washington have a direct line of communication for making sure that the ceasefire is enforced, the ministry said in a statement.
Sergey Rudskoy of the Russian general staff said that, in order to avoid mistakes, the Russian air force would not be carrying out any flights in Syria on Saturday.
Activists in the Damascus suburb of Daraya said they witnessed their first day of calm in four years - despite government media claiming in recent days that al-Nusra was present in the area and it would therefore not be covered by the ceasefire.
Locals insist the extremist group has no presence in Daraya.
"Today people in Daraya are shocked. There were no raids at all, planes were seen hovering over the area, but there were no raids," an activist in the area, who asked to be named just as Fadi, told dpa.
Observers have raised concerns that the exclusion of al-Nusra from the truce could result in continuing fighting in the many areas where it is present alongside more moderate rebel groups.
Further north, a commander of the Jaish al-Mujahedin rebel group, Sami Obeid, told dpa that areas north and west of Aleppo had also witnessed relative calm.
The Observatory reported ongoing fighting in the mountains of north-western Syria, while Islamic State jihadists - who are not covered by the truce - launched a major assault on Kurdish forces near the Turkish border.
At least 70 Islamic State militants and 20 Kurdish fighters and security officers died Saturday after the extremist group launched a widescale offensive against Kurdish forces, the watchdog said
The Kurdish People's Protection Units (YPG), which announced that they were backing the ceasefire earlier this week, said that they were clashing with the extremists in 15 positions near the town of Tel Abyad on the Turkish border.
According to the Observatory the YPG fighters managed to regain back some of the bases they lost in some of Tel Abyad.
The YPG said that the attackers came from the Islamic State stronghold of al-Raqqa to the south and across the Turkish border to the north.
Turkey, which has previously described the YPG as a terrorist organization and has shelled areas held by it, did not immediately comment on the claims.
Islamic State fighters also clashed with government forces further south, on the edges of Syria's central desert, the Observatory reported.
Exchanges of shelling were reported between government and rebel forces in eastern Damascus, while the Observatory said government forces dropped five barrel bombs near the rebel-held city of Jisr al-Shughur in the north-west.
Pro-government sources also said 10 mortar shells landed on the Abbaseen area in government-held central Damascus, near the frontline with rebels in the eastern suburbs.
The Syrian opposition reported breaches of the ceasefire in nine areas during the first hours of its operation, mostly in the form of shelling by government forces.
Syria's war, which started in 2011 after President Bashar al-Assad's forces launched a brutal crackdown against protests, has cost a quarter of a million lives and driven half the country's populations from their homes, according to UN estimates.
UN Syria envoy Staffan de Mistura on Friday told the UN Security Council that, if the ceasefire held and humanitarian access was ensured, he intended to reconvene intra-Syrian peace talks on March 7.
De Mistura put the talks on hold early this month amid opposition fury over a Russian-backed government offensive north of Aleppo.