Syrian warplanes Thursday launched 23 air raids on Mleiha southeast of Damascus, a key rebel bastion President Bashar al-Assad's regime has struggled for weeks to recapture, a monitor said.

Regime ground forces also targeted the Mleiha area with nine surface-to-surface missiles, as troops backed by Lebanon's Shiite Hezbollah battled rebels and their jihadist Al-Nusra Front allies, the Syrian Observatory for Human Rights said.

The Assad regime in late spring began a bid to retake Mleiha, which is strategically located near the airport road and in the besieged rebel region of Eastern Ghouta.

Elsewhere, activists in the rebel-held Al-Hajar al-Aswad neighbourhood in southern Damascus accused the regime of cutting off water supplies for more than two weeks.

"Some 20,000 people live here, mostly women and children. The regime wants to pressure civilians into forcing rebels to sign a truce with the army," activist Rami al-Sayed told AFP.

"People are suffering from inflammations and digestive system diseases because they are drinking dirty water from wells," he added.

Rights groups have frequently accused both sides in Syria's conflict, especially the regime, of using illegal siege tactics as a weapon of war.

On another front, an armed group allied to the jihadist Islamic State of Iraq and the Levant (ISIL) on Wednesday kidnapped two Syrian rebel commanders in Deir Ezzor province.

While rebels seeking Assad's ouster initially welcomed ISIL among their ranks, the jihadists' systematic abuses turned the opposition against them.

Rebels and Islamists have fought ISIL since January, pushing them out of large swathes of the north.

ISIL remains squarely in control of Raqa, and is seeking to expand its influence in oil-rich Deir Ezzor province bordering Iraq. It already controls many of the province's energy fields.