Syria's civil war has ground on in the Middle Eastern country for 13 years, but the capture of a major city could signal a change in the devastating conflict.
Sparked by protests across the Middle East that turned into the Arab Spring, the Assad regime has been fighting multiple rebel groups with the support of Russia and Iran since 2011.
But now, a lightning offensive against government forces that began on Wednesday and focused on the city of Aleppo in north-west Syria has seen rebel forces take territory not ceded since 2016.
What's changed in Syria and how could this affect its roughly 23.5 million people?
Who controls Syria?
Around 70 per cent of Syria is controlled by the government of Syria headed by President Bashar al-Assad, a dictator whose family has controlled Syria since 1971.
Assad's regime is known for rampant human rights abuses and its crackdown on the Arab Spring protests in 2011, which turned into a civil war that swept across Syria and has killed an estimated half-a-million people, according to Associated Press.
The remaining near-third of the country is held by various rebel groups, opposition forces and foreign troops.
Around 6.8 million people fled Syria during the civil war, with many attempting long and arduous journeys to Europe as refugees.
Originally captured by rebel forces in 2012, Aleppo became the site of a months-long siege in 2016 in which Russian air strikes, barrel bombs and other missiles destroyed entire neighbourhoods as the Syrian army attempted to recapture the city of roughly 2 million people.
The government has controlled the city, an ancient trading hub and manufacturing centre prior to the civil war, since then.
Why does Aleppo's capture matter?
Most of Aleppo was under rebel control on Saturday, as well as dozens of nearby towns, the Syrian Observatory for Human Rights said, after a sweeping offensive saw government forces retreat swiftly.
"Hayat Tahrir al-Sham (HTS) and allied factions … took control of most of the city and government centres and prisons without meeting great resistance," the Britain-based war monitor said.
HTS is a jihadist alliance led by Al-Qaeda's formerSyriabranch that, with its allies, has long controlled a rebel enclave in the Idlib region of Syria's north-west.
They also overran Aleppo airport after government forces withdrew, and took control of "dozens of strategic towns without any resistance", the war monitor added.
The fighting has killed at least 327 people, most of them combatants but also including 44 civilians, according to the war monitor.
In a telephone call with his Emirati counterpart, President Bashar al-Assad vowed to defeat the "terrorists" however big their attacks.
Coming after years with few sizeable changes in territory between Syria's warring parties, the takeover has sent ripples throughout the region.
The fighting could be "potentially game-changing", said Charles Lister, a longtime Syria analyst with the US-based Middle East Institute.
"We've been waiting for this" for years, rebel fighter Mohamed Hammadi told AFP in Aleppo's centre.
"We are going to clear all of Syria, God willing," the 29-year-old said.
Dareen Khalifa, a researcher at the International Crisis Group think tank, said the rebels had prepared for months for this offensive.
"They've framed it as a defensive move against regime escalation," Mr Khalifa said, as Syrian government and Russian strikes on the area intensified leading up to the attack.
But HTS and their allies are "also looking at the broader regional and geo-strategic shift", she said.
The rebels launched their attack the same day a Hezbollah-Israel truce came into effect in neighbouring Lebanon.
Who else is involved?
Moscow responded to the fighting in Aleppo with its first air strikes in support of the Syrian government in the area since 2016.
Russian air strikes and military support proved critical to Assad remaining in power, as the key backer of the Assad regime since intervening in the civil war in 2015, alongside Iran.
The Turkish government backs some rebel factions in Syria's north, and earlier demanded an end to strikes on Idlib that "resulted in an undesirable escalation of tensions in the region", the Turkish foreign ministry said.
The US has army bases in the north-east of Syria to guard against Islamic State, and its ally Israel has bombed Hezbollah weapons depots and Syrian forces, among other targets, according to an independent monitoring group.
Israel rarely acknowledges strikes at Aleppo and other government-held areas of Syria.
The US National Security Council spokesman Sean Savett said Syria's "reliance on Russia and Iran", along with its refusal to move forward with a 2015 peace process outlined by the UN Security Council, "created the conditions now unfolding".
Mr Savett added: "At the same time, the United States has nothing to do with this offensive, which is led by Hay'at Tahir al-Sham (HTS), a designated terrorist organisation."
On Sunday, the US and its allies France, Germany and Britain called for "de-escalation" in Syria and urged in a joint statement for the protection of civilians and infrastructure.
"The current escalation only underscores the urgent need for a Syrian-led political solution to the conflict, in line with UNSCR 2254," read a statement issued by the US State Department.
ABC/Wires
