A teenager has been arrested on suspicion of rape and murder after the death of a 13-year-old girl in West Yorkshire, police have said.

Officers were called to a flat on Sheepridge Road in Huddersfield on Monday night to reports that a girl was unresponsive. West Yorkshire police said the victim died in hospital and her death was being treated as “unexplained” after a postmortem examination.

A 16-year-old boy from Huddersfield was arrested on suspicion of murder and rape and is in custody.

The suspect was also arrested on suspicion of another offence of rape relating to a 16-year-old girl from a separate incident elsewhere in the Kirklees district, the force said on Thursday.

DCI Stacey Atkinson said: “A postmortem was not able to determine how she died, and we continue to treat her death as unexplained at this time, pending more inquiries.

“Those inquiries are complex and are likely to be lengthy as we work to fully understand the circumstances of the girl’s death.”

West Yorkshire police said: “Police were called by the ambulance service to an address on Sheepridge Road, Huddersfield at 11.36pm on Monday 11 August to a report that the teenage girl was unresponsive.

“The 13-year-old was taken to hospital where she sadly died in the early hours of Tuesday morning. A 16-year-old boy, from Huddersfield, was arrested on suspicion of murder and rape, remains in police custody.

“A postmortem examination was conducted [on Wednesday] which concluded the girl’s death was unexplained pending further investigation.”