Islamic State (Isis) has released pictures that purport to show a wheelchair-bound militant seemingly preparing to execute a man accused of spying in Libya.

The images were released on 2 February by an IS (Daesh) branch in Libya's Tripoli province, Wilayat Tarabulus, and are captioned "the execution of spies in the city of Sirte", Newsweek Europe reported.

The images show two of the accused lying bloodied on the ground in a desert and another crucified on a wooden structure with a sign saying "spy" attached to his abdomen. All three wear the orange jumpsuits worn by victims in previous IS execution videos and images.

An image shows the man crucified kneeling by a militant in a wheelchair. A rope tied around his midriff is attached to the wooden structure, where an IS flag is propped. The three men are only identified as "spies".

IS released the pictures following reports that a secret sniper is picking off its commanders in the city of Sirte, which it seized late in 2014 amid the chaos the country descended into after dictator Muammar Gaddafi was ousted in a Nato-backed rebellion.

The foothold established by the group in Libya in January prompted US Secretary of Defence Ashton Carter to announce the Pentagon is "developing options" for potential military action against IS in Libya.

Amid reports that Western countries may be preparing to launch air strikes against IS positions in Sirte, the group has in recent weeks launched a series of attacks against oil facilities.