A long-running civil war appeared to have come to a head Sunday when Syrian insurgents entered the capital city of Damascus and President Bashar Assad fled the country as his government appeared to have collapsed.

Rami Abdurrahman — who heads the Britain-based Syrian Observatory for Human Rights, an opposition war monitor — told the Associated Press that Assad took a flight Sunday out of Damascus. Two senior Syrian army officers also told Reuters that Assad flew out of Damascus Sunday for an unknown destination. The White House indicated to CBS News it was unaware of Assad’s whereabouts. 

Syrian Prime Minister Mohammed Ghazi Jalali said early Sunday that he had remained in Damascus and said the government was ready to “extend its hand” to the opposition and hand over its functions to a transitional government, the AP reported. 

Abdurrahman earlier said insurgents had been active in the Damascus suburbs of Maadamiyah, Jaramana and Daraya. He added that opposition fighters were also marching from eastern Syria toward the Damascus suburb of Harasta.  

Hassan Abdul-Ghani, an insurgent commander, also claimed early Sunday morning local time that insurgent forces had “fully liberated” the central city of Homs, Syria’s third-largest, Reuters reported.      

What is happening with the war in Syria?

Thousands of people fled from the area amid the dramatic escalation in the civil war, which had simmered without major advances by either side for years, until the rebels mounted a shock offensive about two weeks ago.

The rebels took complete control of another city, Hama, and about a week after they began a sweeping raid across the north of the country. The first major prize in their offensive was seizing control of Aleppo a week ago, which was long Syria’s second most populous city. 

Their sudden advance has taken many watching the long-simmering conflict by surprise, and SOHR says over 820 people have been killed since it started, including more than 100 civilians.

Syrian rebels said the objective “remains the overthrow” of Assad

The war in Syria began in 2011 when a pro-democracy uprising calling for the end of Assad’s long reign escalated quickly into a brutal civil war. Since then, the conflict has killed more than 500,000 people and displaced some 12 million from their homes.

The war appeared to have stalled after Assad’s government regained control over many cities with the help of Russia and Iran, in addition to the powerful Iranian proxy group Hezbollah in Lebanon. Some northern and eastern areas of the country have remained under the control of Kurdish-led, U.S.-backed rebel groups. The current offensive, however, has been led largely by the militant group Hayat Tahrir al-Shams (HTS), which has tried to publicly distance itself from its jihadist roots as a regional branch of al Qaeda.

With other conflicts currently occupying Assad’s backers Iran, Russia and Hezbollah, the rebel forces are believed to have seen an opportunity to renew their fight against his army.

The leader of HTS told CNN in a recent interview that the goal of the offensive is to remove Assad from power.

“When we talk about objectives, the goal of the revolution remains the overthrow of this regime,” Abu Mohammad al-Jawlani told CNN. “The seeds of the regime’s defeat have always been within it… the Iranians attempted to revive the regime, buying it time, and later the Russians also tried to prop it up. But the truth remains: this regime is dead.”

Syrian rebel offensive worsens humanitarian crisis

Tens of thousands of civilians have fled the recent fighting, many of them heading to Raqqa province, which is held by the U.S.-backed Syrian Democratic Forces (SDF). 

Despite a deal to allow safe passage for those fleeing Aleppo province, SDF sources told CBS News that over 120 vehicles carrying hundreds of civilians were attacked by different Syrian Islamist groups on their journey. Local authorities say the humanitarian situation for those arriving in safe areas is dire.

Some 136 schools in Raqqa and 63 schools in the city of Tabqqa have been turned into makeshift shelters for IDPs. Raqqa Stadium, which was once used as a prison by ISIS militants when they controlled the territory, has also been turned into a camp to offer displaced civilians some shelter from the cold weather.

“The situation is catastrophic,” Zhwan Mullah, a member of the local crisis response team, told CBS News. “The number of IDPs is much larger than we can assist. U.N. and NGO support so far has been very insignificant.”

Saeed Muhammad Hassan, 53, fled to Raqqa from near Aleppo. On his way, he was separated from his wife, Sabah. Hassan, like an increasing number of civilians who’ve been separated from loved ones during their evacuation from areas hit by the fighting, approached local radio stations to put out an appeal to be reunited with Sabah.

“Many people are approaching us via different channels, looking for missing family members who have gone silent on the road to safety,” Sirwan Haji Birko, the head ARTA FM radio, told CBS News. “We try to help as much as we can to find missing ones, on radio and on our social media platforms.”

The Associated Press contributed to this report.

Haley Ott

Haley Ott is the CBS News Digital international reporter, based in the CBS News London bureau.