The Syrian army has discovered a long tunnel underneath a rebel-held eastern Damascus district, the state-run TV said Sunday.

The tunnel, which is 600 meters long and 17 meters deep, was dug by the rebels in the eastern suburb of Jobar, the TV said, adding that the tunnel is provided with ventilation system and lightening.

Jobar fell to the rebels in summer 2013 and the government troops mounted an offensive for the recapture of this district last September.

One of the hurdles facing the government troops' progress in Jobar is believed to be the network of intractable tunnels dug by the rebels under Jobar to facilitate their movement in other rebel-held areas in the Eastern Ghouta countryside of Damascus.

The rebels in Jobar are responsible for much of the mortar attacks against the residential districts of Damascus.

Rocket and mortar fire from Jobar killed at least 12 people and wounded 37 others in Damascus last Saturday.

The rebel-held areas in eastern Damascus are also subject to the government troops' artillery and airstrikes.

Earlier in the day, Syrian airstrikes against the eastern suburb of Douma, near Jobar, killed over 80 people, according to the Syrian Observatory for Human Rights watchdog group.

According to the Observatory, the Syrian conflict has killed more than 240,000 people.