Syria’s conflict has killed more than 310,000 people, uprooted over half the population and left much of the country in ruins since it erupted almost six years ago.
Here are some key statistics:
Those killed included 90,000 civilians, of which 16,000 were children, the Britain-based monitor said.
And almost one million Syrians are besieged by the warring parties, according to UN aid chief Stephen O’Brien.
The war has forced 4.8 million people to flee Syria, according to the United Nations High Commissioner for Refugees.
Neighbouring Turkey has taken in more than 2.7 million Syrians, the UNHCR says, and is now the main host country.
Jordan, which the UNHCR says has taken in 655,000 Syrians, says it has accepted considerably more, at 1.4 million.
At least another 228,000 Syrians have taken refuge in Iraq and 115,000 in Egypt, the refugee agency says.
Syrian refugees have in increasing numbers travelled to or attempted to reach Europe, making the perilous journey overground or by sea.
It said more than 17,700 people are estimated to have died in custody since the conflict began.
But it said the real figure is much higher, pointing to tens of thousands of forced disappearances.
The Observatory, for its part, says at least 60,000 people have died over five years from torture or harsh conditions in regime prisons.
And several thousand have died over the same period in prisons run by rebel groups or jihadists, it says.
In February 2016, UN investigators accused the regime of “extermination” in its jails and detention centres.
The education and health systems are in ruins.
In 2015, a coalition of non-governmental organisations said Syria was living almost without electricity, with 83 percent of lighting no longer working.
The study also said the Syrian economy contracted by 55 percent between 2010 and 2015.