Islamic State militants have beheaded four teenage boys and young men in the Syrian city of Raqqa, accusing them of supplying information to the US-led coalition fighting the terror group.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said that Isil had accused the young men of "photographing sites and handing information to the crusader coalition causing bombing and the death of Muslims".

The report was confirmed by Raqqa is Being Slaughtered Silently (RBSS), a campaign group whose members risk their lives to smuggle news of Isil’s atrocities to the outside world.

Raqqa, once a relatively liberal city, became Isil’s de facto capital in 2014. Its residents are now subject to the group’s brutal, sharia-inspired rule and beheadings are commonplace.

So are other punishments drawn from obscure Islamic teachings, such as a diktat suggesting that gay men are pushed from the tops of buildings.