The latest flareup in Syria's long civil war comes after insurgents opposed to Syrian President Bashar Assad over the past days captured large parts of the northern city of Aleppo, as well as towns and villages in southern parts of the northwestern Idlib province.

The offensive is being led by Hayat Tahrir al-Sham (HTS), an armed group, as well as an umbrella group of Turkish-backed Syrian militias called the Syrian National Army. For years, both have entrenched themselves in northwest Idlib province and parts of northern Aleppo, as the battered country reeled from years of political and military stalemates.

The civil war between the Syrian army and the array of armed opposition groups seeking his overthrow has killed an estimated half-million people over the past 13 years.

Syrian state media SANA on Wednesday said insurgents retreated some 20 kilometres (12 miles) from government-held Hama, Syria's fourth largest city, as government troops backed by Russian airpower entrenched themselves in the outskirts. Fierce fighting has raged for days as Damascus fears that the insurgents will make their way into the city as they did over the weekend into Aleppo.

A Syrian photographer working for the German news agency DPA was killed in an airstrike near the city of Hama, the agency said Wednesday.  Anas Alkharboutli, 32, has long documented Syria’s civil war, which started in 2011. He has worked for DPA since 2017.

If the insurgents seize Hama city and control the province, it could leave the coastal cities of Tartous and Lattakia isolated from the rest of the country. Lattakia is a key political stronghold for Syria's Alawite community and a strategic Russian naval base.

Tens of thousands have been displaced by the fighting, which started last week, Geir Pedersen, the U.N. special envoy for Syria, said Tuesday.

“If we do not see de-escalation and a rapid move to a serious political process, involving the Syrian parties and the key international players, then I fear we will see a deepening of the crisis," Pedersen said in an address to the U.N. Security Council. "Syria will be in grave danger of further division, deterioration, and destruction."

Turkey, which backs Syria's opposition, has called on Assad to reconcile with the armed groups and include them in any political solution to end the conflict.

Ankara has been seeking to normalise ties with Syria to address security threats from groups affiliated with Kurdish militants along its southern border and to help ensure the safe return of more than 3 million Syrian refugees. Assad has insisted that Turkey’s withdrawal of its military forces from northern Syria be a condition for any normalisation between the two countries.

Damascus views the insurgents as terrorists, and Assad has vowed to respond to the insurgency with an iron fist.

Turkish and Iranian officials met earlier this week, in a bid to solve to deescalate the flareup. Arab countries bordering Syria have expressed their concern of the conflict's regional impacts, and have backed the Syrian president.