The Syrian troops have started a wide-scale offensive on a key rebel-held Syrian city northeast of the capital Damascus, the state-news agency SANA reported Saturday.

The troops started the offensive on the city of Adra, fully besieging the town and killing many "terrorists," said SANA, spelling no further details.

Meanwhile, the oppositional Syrian Observatory for Human Rights said the Syrian air force carried out eight airstrikes against Adra and the nearby Tal Kurdi area Saturday, adding that the Syrian army and its loyal troops clashed with an array of rebel groups in Adra, mainly the al-Qaida-linked Nusra Front.

The city is administratively part of the Damascus' sprawling suburb of Douma, which has for long fallen to an array of rebel militias. Adra, home for more than 20,000 Syrians, contains the site of Syria's largest industrial city, which is located east of the town. The industrial zone's area is around 7,000 hectares, with half being designated for services and the other half for industries.