Here are some key statistics:
– Huge death toll –
The Britain-based Syrian Observatory for Human Rights says it has recorded the deaths of 321 358 people since the conflict began with anti-government protests in March 2011. Those killed included 96 000 civilians, of which over 17 000 were children, the monitor said.
In a country with a pre-war population of 23 million, the United Nations estimates that 6.6 million people have been internally displaced by the fighting.
The UN High Commissioner for Refugees (UNHCR) says 4.7 million people live either in besieged cities or hard-to-access areas.
– Refugees –
The war has forced 4.9 million people to flee Syria, according to the UNHCR. Neighbouring Turkey, the main host country, has taken in more than 2.9 million Syrian refugees.
It is followed by Lebanon, which the UN says hosts around one million Syrians — one in four of the Lebanese population. The Lebanese government says as many as 1.5 million Syrians are in the country.
In Jordan, where the UNHCR says it has registered 630,000 Syrians, the government says it is hosting 1.4 million.
At least another 225,000 Syrians have taken refuge in Iraq and 137,000 in Egypt, the refugee agency says.
It adds that around 90 percent of Syrian refugees are living in poverty and at least 10 percent are considered “extremely vulnerable.”
– Imprisoned, tortured –
In February, Amnesty International said Syrian authorities hanged around 13,000 people between 2011 and 2015 at the infamous Saydnaya prison near Damascus. It said a further 17,700 people had died in custody since the conflict began.
The Observatory says at least 60,000 people have died from torture or harsh conditions in regime prisons since 2011. The monitor says half a million people have spent time in regime jails since the start of the conflict.
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.
– Economy in ruins –
Experts say the conflict has set Syria’s economy back by three decades and devastated its infrastructure. The education and health systems are in ruins.
By 2015, 83 percent of Syria’s electric grid was out of service, according to a coalition of 130 non-governmental organisations.
More than four-fifths of the population lives in poverty, according to an April 2016 study by the United Nations and Britain’s Saint Andrews University.
The study also said that Syrian business activity shrank by 55 percent between 2010 and 2015.