Syrian rebels claim they have downed a fighter jet in what would be a major coup for the opposition, but the regime has seized the upper hand in Aleppo, where it advanced into a new rebel-held district.

Government forces also bombarded areas around Damascus and launched a wide sweep of the capital, including its once-bustling historic Old City, while shocking videos emerged showing alleged rebel atrocities in the Aleppo area.

State media said a military plane on a training mission crashed into the east of the country after suffering a malfunction and the pilot had ejected.

But the Free Syrian Army, which has been calling for the international community to arm it with anti-aircraft weapons as it battles escalating regime attacks from the sky, claimed it shot down the Russian-made MiG in the eastern province of Deir Ezzor.

“With God’s help, a MiG 23 plane was downed in Muhasen on Monday morning, by the hands of the Ahfad Mohammed (Grandchildren of Mohammed) Brigade,” said Captain Abul Laith, whose group is part of the FSA.

Another group calling itself the Revolutionary Youth of the Land of the Euphrates distributed a video showing a man identified as pilot Mufid Mohammed Suleiman, surrounded by three armed men.

“My mission was to bomb the town of Muhasen,” said the purported pilot.

FSA spokesman Kassem Saadeddine said he knew the pilot and identified him as Colonel Mufid Mohammed Sleiman, a member of the Alawite minority community of President Bashar al-Assad and his inner circle.

“He is a member of a squadron I used to fly with … before I defected,” Saadeddine told AFP via Skype. “I served with him for 15 years, and he is a staunch enemy of the revolution.”

If confirmed, the attack would be the first time the rebels have succeeded in downing a Syrian plane since Assad’s regime launched an increasingly brutal crackdown on protests 17 months ago.

At least 103 lost their lives in fighting on Monday, according to the Syrian Observatory for Human Rights.

The opposition has accused the regime of increasingly resorting to firing from fighter planes, particularly on the second city of Aleppo, which has witnessed some of the fiercest fighting in recent weeks.

The umbrella opposition group the Syrian National Council has issued a new appeal for the establishment of no-fly zones similar to those set up over Libya during last year’s conflict.

More than 21,000 people have been killed since March last year, with fighting escalating after the failure of outgoing international envoy Kofi Annan’s peace plan and the regime hit by an increasing number of defections by high-ranking officials.

The latest to flee on Monday was Syria’s top representative at the UN Human Rights Council.

Meanwhile, foreign ministers of Muslim states gathered in Jeddah, with the Organisation of Islamic Cooperation expected to suspend Syria, despite divisions between host Saudi Arabia and regional rival Iran.