BEIRUT (Reuters) - Islamist fighters struck the Syrian capital with at least 38 rockets on Sunday, killing seven people, a monitoring group said, in one of heaviest attacks on Damascus in over a year.

State media confirmed the attack and said at least four people were killed. It said the army was retaliating.

The Saudi-backed Islam Army, based in the eastern Ghouta region near Damascus, had warned earlier that it would hit back against an air strike last week in Ghouta in which more than 40 people were killed.

Damascus residents said Sunday's rockets seemed to be mortars and Katyusha.

Rami Abdulrahman, head of the Syrian Observatory for Human Rights which monitors the violence in the country, said this was the heaviest attack on the capital for more than a year.

The Syrian army was shelling the rebel-held town of Douma where the Army of Islam is powerful, Abdulrahman said. Douma lies on one of the main roads linking the capital with Homs city further north.

Reuters could not independently verify the reports.

Syria's air force has launched daily air strikes in the civil war, which started after security forces cracked down on pro-democracy protests in 2011. At least 200,000 people have been killed in the conflict.

Throughout Damascus has been relatively calm, shielded from the war since government forces pushed the rebels back in 2013.

(Reporting by Mariam Karouny; Editing by Raissa Kasolowsky)