Four men have been arrested on suspicion of raping a 19-year-old woman in an alleyway, police have said.
The four men, aged 37, 31, 25 and 20, have been held by police after a woman was attacked at 10pm on Saturday in Southsea, Hampshire.
Three of the men have been released “pending further inquiries”, detectives said.
One suspect, the 31-year-old, has remained in police cells.
Detectives said they are not linking the attack, which took place over the Bank Holiday, to any other assaults.
The force added the woman did not know her attacker and was receiving specialist support.
A spokesman for Hampshire Police said: “Three men aged 20, 25, and 37 who were arrested on suspicion of rape have been released without charge, but remain under investigation.
“A fourth man, aged 31, also arrested on suspicion of rape remains in custody at this time.
“At this time detectives are not linking this report to any other ongoing investigations.”
Detective Inspector Emma Crute called on people to get in touch if they saw anything connected to the attack.
She said: “We are continuing to carry out enquiries and I’m still keen to hear from any residents who may have heard or seen something that could assist our investigation.
“This incident took place on a busy Saturday night at the start of a Bank Holiday weekend and we believe there would have been a lot of people out and about in the area at the time”.
Anyone with information is asked to call 101.