Detective Superintendent Sue Coombs said: “We are also sharing a still image of a van which was in the vicinity of the incident and may have witnessed something vital.

“To be clear, we think those vehicle’s occupants are witnesses, and in no way suspected of being involved. However, we still need to speak to those people as soon as possible to confirm what information they might hold.”

Police said that a verbal argument had broken out between children and it had rapidly escalated into violence, with unconfirmed reports that Ava had been stabbed in the neck.

Yesterday floral tributes were still being left in the city centre while a large cordon remained in place along Church Alley, School Lane and Fleet Street where the suspects are thought to have fled on foot.

Detective Coombs said Ava’s family was being supported by specialist officers and added: “Merseyside Police is absolutely determined to bring those responsible to justice. Today we are also issuing new images of Ava on behalf of her family.”

On Friday, Notre Dame Catholic College in Liverpool paid tribute to Ava, their former pupil, as a “much loved, valued and unique member” of the school’s family.

Members of the public with information are urged to contact Merseyside Police Contact Centre on Facebook quoting reference 21000820789, call 101 or reach the independent charity Crimestoppers anonymously on 0800 555 111.