A teenage boy arrested in connection with the suspected drug death of a 15-year-old girl remains in police custody.
Rose Farley, from Liverpool, fell ill at a birthday party on Friday evening and died at Alder Hey Children's Hospital during the early hours of Saturday.
Detectives investigating the incident detained a 16-year-old youth from Liverpool on Sunday on suspicion of supplying drugs. He was taken into custody for questioning where he remains, Merseyside Police said.
Miss Farley's death comes amid reports that her drinks may have been spiked, and just days after Merseyside Police warned youngsters of a deadly ecstasy-type drug circulating in the area.
A spokeswoman for the force said the death of the youngster, who is from the West Derby area of Liverpool, is still being treated as "unexplained". She added that although a post-mortem examination had been carried out, the cause of Miss Farley's death has been withheld pending toxicology results.
Detective Superintendent Tim Keelan of Merseyside Police said: "At this stage it is too early to draw conclusions about the cause of death and it is unhelpful to speculate. The implication that this may be drug-related is just one of the lines of inquiry that our comprehensive investigation is looking at.
"That said, I would like to take this opportunity to warn people about the dangers of taking illegal substances. The effects of drugs are not always immediately apparent or can be delayed. This can sometimes result in people taking more in order to speed up the effects. This can have devastating results, one of which can be death."
The force had warned of a potentially lethal new drug on the streets in the form of pink pills, known as pink ecstasy, Dr Death or Pink McDonalds - because the pills are embossed with an M.
The warning was issued following the sudden deaths of two men in 24 hours in Cambridgeshire earlier this week. A man also died in similar circumstances in Bournemouth, Dorset, on May 21.
Emergency workers were called to Miss Farley's home during the early hours of Saturday morning. She was rushed to hospital but died just after 5am. Anyone with information is asked to contact detectives on 0151 777 4065 or call Crimestoppers anonymously on 0800 555 111.