A new nationwide ceasefire between Syrian government forces and rebel groups appears to be largely holding.
However, isolated clashes have been reported since the truce, brokered by Russia and Turkey, went into effect at midnight (22:00 GMT) on Thursday.
The deal includes many rebel factions, but not the jihadist group Islamic State (IS) or the Kurdish YPG militia.
The truce is intended to be a prelude to peace talks between the warring parties in Kazakhstan next month.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said most of Syria was calm overnight. But it reported “fierce clashes” between rebels and government forces in the northern province of Hama.
SOHR director Rami Abdel Rahman told AFP news agency: “Small rebel groups and armed loyalists are seeking to destroy the truce because it puts an end to their presence.”
The new kingmaker – Lyse Doucet, BBC chief international correspondent
This deal was declared before it was done and dusted. Seven groups said to have signed up include Ahrar al-Sham, which Moscow and Damascus have always described as terrorists. Ahrar Al-Sham says it has “reservations”. Do they have anything to do with backers like Saudi Arabia and Qatar?
But a new top table has been forged before a new US president enters the scene. Russia is confirmed as the foreign force which matters. Turkey displaced the US as kingmaker on the other side. It has bargaining chips and, most of all, wants to stop the sway of Syrian Kurdish forces, who are US allies.
Many opposition fighters will welcome a pause after their stinging defeat in Aleppo. But they and Turkey still want President Assad to step down. That conflicts with Iran, the other key player, as well as Mr Assad’s own circles. But that’s for the next round in this new great game which could be talks in Astana, in Russia’s orbit.
Residents of the Eastern Ghouta region outside Damascus also said they heard gunfire less than two hours after the ceasefire took effect. Other isolated incidents were reported in the north-western province of Idlib.
Later on Friday, fighting was reported in the Wadi Barada region, the location of springs which supply the capital with drinking water.
Meanwhile, Turkish military officials said Russian aircraft had carried out three air strikes against IS militants around the northern town of al-Bab.
The strikes appeared to be the first Russian support for a Turkish-backed rebel offensive aimed at recapturing the last IS stronghold in Aleppo province.
Russia has carried out an air campaign in support of President Bashar al-Assad since September 2015, while Turkey is a major supporter of the rebellion.
Russia takes centre stage – Jonathan Marcus, BBC diplomatic correspondent
If the fall of Aleppo to government forces demonstrated that Russia and its Syrian allies now hold the military initiative, then this new ceasefire deal suggests that Moscow has a good measure of the diplomatic momentum as well.
Unlike previous ceasefires, this has not come out of US and Russian bilateral spadework, but from a new understanding between Moscow and Ankara.
But this new agreement relates to only one of Syria’s conflicts. It does not encompass IS or the main rebel grouping linked to al-Qaeda. Even President Putin describes the deal as fragile.
The real question may be where the Russian-Iranian military effort will focus next. The deal nonetheless marks a transitional moment in the conflict, with the US tacitly acknowledging failure in Syria and Turkey signalling to the rebels that it is Ankara’s strategic interests that now take precedence.
Will the ceasefire hold?
The diplomatic noises are encouraging, and even the rebel groups involved have suggested it could succeed.
However, previous initiatives this year quickly collapsed.
Syrian Foreign Minister Walid Muallem said there was “a real chance to reach a political settlement to end the bloodshed and establish the future of the country”.
The fact that the rebels have been losing ground may help.
Who is included in the deal?
On the one side, Syrian government forces, allied militias and the Russian military.
On the other, a loose alliance of moderate rebel factions that operate under the banner of the Free Syrian Army (FSA), plus several other groups.
The Russian defence ministry listed seven of the “moderate opposition formations” included in the truce as Faylaq al-Sham, Ahrar al-Sham, Jaysh al-Islam, Thuwwar Ahl al-Sham, Jaysh al-Mujahidin, Jaysh Idlib and Jabhah al-Shamiya.
Ahrar al-Sham and Jaysh al-Islam are powerful Islamist groups that Russia has previously described as terrorist organisations.
A spokesman for Ahrar al-Sham also told Reuters news agency that the group had “reservations” and had not signed the deal.
Who is not included?
Jihadists. So-called Islamic State “and the groups affiliated to them” are not part of the agreement, according to the Syrian army.
Jabhat Fateh al-Sham, which was known as al-Nusra Front until it broke off formal ties with al-Qaeda in July, is also excluded. However, some rebel officials told Reuters that the group was included in the deal, giving a hint of the complications that lie ahead.
This is because JFS is part of a powerful rebel alliance that controls much of Idlib province.
The FSA also said the deal did not include the Kurdish Popular Protection Units (YPG). The militia, which has captured large swathes of north-eastern Syria from IS with US support, is not officially aligned to either the opposition or government, but is designated a terrorist organisation by Turkey.
What are the terms of the deal and where does it cover?
It is nominally nationwide, although that really only covers the areas where the sides who have signed up have a presence.
Looking at the map, there are large swathes under both IS and Kurdish control.
One area that is included is the Eastern Ghouta, where government forces have been advancing in recent months.
Under the terms of the deal, the peace talks would begin within a month of the truce taking effect – and holding – and would be held in Astana.
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