Dec 02, (V7N) - Syrian President Bashar al-Assad sought to shore up support from his allies Sunday, after a monitor said a shock rebel offensive saw government forces lose control of Aleppo for the first time since the start of the country's civil war.

An Islamist-dominated rebel alliance attacked forces of the Iranian- and Russian-backed government on Wednesday, the same day a fragile ceasefire took effect in neighbouring Lebanon between Israel and Iran-backed Hezbollah after two months of all-out war.

The Islamist Hayat Tahrir al-Sham (HTS) group and allied factions now "control Aleppo city, except the neighbourhoods controlled by the Kurdish forces", Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights, told AFP.

For the first time since the civil war started more than a decade ago, the country's second city "is out of control of Syrian regime forces", he said.

Iran's Foreign Minister Abbas Araghchi travelled to Damascus on Sunday to meet Assad, saying before his departure that Tehran would "firmly support the Syrian government and army", Iranian state media reported.

After the talks, Assad emphasised "the importance of the support of allies and friends in confronting foreign-backed terrorist attacks".

Araghchi landed late Sunday in Ankara, where he was expected to meet with Turkish Foreign Minister Hakan Fidan on Monday before talks with President Recep Tayyip Erdogan.

Syrian and Russian aircraft had staged deadly strikes in support of government forces earlier Sunday, according to the Observatory.

It said strikes killed at least 12 people in Aleppo and nine civilians in the rebel bastion of Idlib.

Russia's military confirmed it was helping Syrian government forces "repel terrorist aggression in the provinces of Idlib, Hama and Aleppo".

The Russian and Syrian warplanes had targeted "a gathering of terrorist organisation commanders and large groups of their members" in Aleppo province, killing "dozens", according to a military statement carried by Syrian state news agency SANA.

It also said warplanes destroyed a large vehicle convoy carrying "terrorist" ammunition and equipment in Idlib.

In the province on Sunday, bodies lay in a hospital and vehicles were torched in the street, AFP images showed.

Resident Umm Mohamed said strikes in the area had killed her daughter-in-law, who left behind five children, including a wounded little girl.

"Thank God their injuries were minor," she told AFP from hospital.

In 2016, the Syrian army -- supported by Russian air power -- recaptured rebel-held areas of Aleppo, a city dominated by its landmark citadel.

Damascus also relied on Hezbollah fighters to regain swaths of Syria lost to rebels early in the war, which began in 2011 when the government crushed protests. But Hezbollah has taken heavy losses in its fight with Israel.

Before this offensive, HTS, led by Al-Qaeda's former Syria branch, already controlled swaths of the Idlib region, the last major rebel bastion in the northwest.

HTS also held parts of the neighbouring Aleppo, Hama and Latakia provinces.

The latest fighting has killed more than 412 people, mostly combatants but also including at least 61 civilians, according to the Observatory, which has a network of sources inside Syria.

The Observatory said rebel advances met little resistance.

It said Sunday the army strengthened its positions around Syria's fourth largest city Hama, about 230 kilometres (140 miles) south of Aleppo, and sent reinforcements to the north of the surrounding province.

Rebels have taken dozens of towns across the north, including Khan Sheikhun and Maaret al-Numan, roughly halfway between Aleppo and Hama, the Observatory said.

The air strikes on parts of Aleppo were the first since 2016. One resident told AFP most locals were "holed up at home".

Aaron Stein, president of the US-based Foreign Policy Research Institute, said "Russia's presence has thinned out considerably and quick reaction air strikes have limited utility".

He called the rebel advance "a reminder of how weak the regime is".

Aron Lund of the Century International think tank said: "Aleppo seems to be lost for the regime, and unless they manage to mount a counteroffensive soon, or unless Russia and Iran send much more support, I don't think the government will get it back."

"And a government without Aleppo is not really a functional government of Syria," he added.

The United States and its allies France, Germany and Britain called Sunday for "de-escalation" in Syria, and 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, referencing the 2015 UN resolution that endorsed a peace process in Syria.

The United States maintains hundreds of troops in northeast Syria as part of an anti-jihadist coalition.

Parallel to the HTS offensive, pro-Turkey factions in northern Syria attacked Kurdish fighters in Aleppo province on Sunday, with the Observatory saying they seized the strategic town of Tal Rifaat and nearby villages.

UN envoy Geir Pedersen said the "latest developments pose severe risks to civilians and have serious implications for regional and international peace and security".

END/WD/RH/