Daesh fanatics 'called people to watch' as they executed 20 local men in a Roman ampitheatre in the ancient Syrian city of Palmyra, the Daily Mail quoted a watchdog as saying on Thursday.

The men were shot dead in the restored ruin, which had been used for an annual festival in the city, in front of the crowd on Wednesday.

The murdered locals were accused of being government supporters, according to a report from the Syrian Observatory for Human Rights.

'IS (Daesh) executed 20 men by firing on them in front of a crowd gathered in Palmyra's Roman theatre, after accusing them of fighting for the Syrian regime,' Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said.

He added: 'Daesh (Daesh) gathered a lot of people there on purpose, to show their force on the ground.'