A third teenage boy has been charged over a series of alleged armed robberies across Sydney last month.

Detectives from the State Crime Command’s Robbery and Serious Crime Squad established Strike Force Marril to investigate a series of armed robberies at service stations in January.

On Tuesday 2 January 2018, three males entered a service station at Kings Langley and threatened the male attendant with a shortened firearm and a sword; demanding cash.

During the incident, the attendant was allegedly struck with the sword, which partially severed his thumb.

On Wednesday 3 January 2018, a service station attendant at Toongabbie was approached by three males armed with a shortened firearm and a bladed weapon, who demanded cash.

On Monday 8 January 2018, three males threatened the attendant with a shortened firearm and a bladed weapon at a service station at North Ryde, demanding cash.

In each incident, the group allegedly stole cash and other goods before running from the store.

Two teenage boys were previously charged by strike force investigators. They remain before the courts.

Following further inquiries, detectives arrested a 15-year-old boy at Wentworthville about 1.20pm yesterday (Monday 26 February 2018).

He was taken to Granville Police Station and charged with robbery armed with two counts of in company rob while armed with dangerous weapon, offensive weapon cause wounding/grievous bodily harm, and robbery armed with offensive weapon.

Police will allege in court that the boy was also involved in an armed robbery at a tobacconist at Prospect on Saturday 17 February 2018.

The boy was refused bail and appeared at a children’s court, where he was formally refused bail to reappear on Friday 13 April 2018.

Investigations under Strike Force Marril are continuing.