Syrian rebels took control of most of a strategic army base in northern Syria after a fierce firefight with President Bashar al-Assad's forces on Wednesday, a monitoring group said.

The military complex, known as Base 80, is tasked with securing the nearby Aleppo international airport as well as the Nayrab military airport.

"Fierce clashes pitting troops against rebels loyal to Al-Nusra Front, Liwa al-Tawhid, Al-Muhajireen and other groups raged near Base 80, most of which has come under insurgent control," said the Syrian Observatory for Human Rights.

The fighting came a day after rebels in Aleppo province seized a military airport at Al-Jarrah and launched an assault on other air bases in the area, including the Aleppo international airport, closed since January 1.

Dozens of fighters and troops have been killed in the fighting, the Britain-based Observatory said.

Activists have said Aleppo's insurgents shifted their focus from targets in the provincial capital to air bases because they are a source of ammunition and weaponry, and to put out of action warplanes used to bomb rebel bastions.

In Aleppo city itself, meanwhile, there was no supply of electricity or water Wednesday for a fourth day in a row, said the anti-regime Aleppo Media Centre, warning of a "humanitarian disaster" in what was once Syria's commercial hub.

Commenting on the rebels' advance in Aleppo province, Observatory director Rami Abdel Rahman said the army may be giving up on parts of northern Syria, in order to secure the centre.

"The army is barely resisting the rebels' advance on bases in the north. Meanwhile, it is resisting with ferocity the insurgents in Daraya (southwest of Damascus) and Homs (in central Syria)," Abdel Rahman told AFP.

"The regime understands it cannot survive a transition without securing some land to bargain with," he added.

Despite the advances, regime warplanes remained active in Aleppo province on Wednesday, carrying out bombing raids on the outskirts of the town of Sfeira, southeast of Aleppo, and Al-Bab, northwest of Syria's second city, said the Observatory.

Further south, the air force launched at least 10 bombing raids on rebel-held Deir al-Asafeer near Damascus, according to the Syrian Revolution General Commission, a grassroots network of activists.

Meanwhile, on the eastern and western edges of the central city of Homs, rebels clashed with troops on two main highways, a rebel commander said.

Arraba Idriss told AFP via Skype that the insurgents are trying to "ease the pressure on people trapped in districts that have been besieged and bombarded" for some eight months by the army.

At least 190 people were killed in violence across Syria on Wednesday, said the Observatory, among them 79 troops and 76 rebels, making it an exceptionally bloody day for fighters on both sides.