The Syrian army has found a mass grave containing the bodies of 42 civilians and soldiers executed by the so-called Islamic State jihadist group in Palmyra, state media reported.

"The Syrian army ... uncovered a mass grave of officers, soldiers, members of the popular committees and their relatives," an army source also said, adding that 24 of the victims were civilians.

Last Sunday, troops loyal to Syrian President Bashar Al Assad drove the Islamic State group from the ancient city, renowned for its monument and artefacts, almost a year after it was overrun by the militants.

Syrian state news agency SANA said the grave, which contained many women and children, was in the north-eastern edge of Palmyra.

Some of the bodies had been beheaded.

The Syrian Observatory for Human Rights which monitors the five-year-old Syrian conflict through a network of sources on the ground, said that Islamic State had killed a number of people at an earlier time and buried them on the outskirts of the city.