Two men pulled a woman off the street and sexually assaulted her.
The woman, who is in her 50s, was targeted in Ravenstone Road,
Coalville.
The men approached her and dragged her from the pavement to an area behind an advertising hoarding, where what police described as a "serious" sexual assault took place.
The attack happened at 10.15pm on Friday, June 7. The woman reported it to police a week later.
The attackers are black, approximately 6ft, aged 30 to 40 and are of muscular build. They were both wearing dark clothing.
Detective Sergeant Neil Holden said: "Attacks such as this one are very rare, and this appears to be an isolated case.
"We would like to speak to anyone who was in the area that evening.
"There are bus stops on either side of Ravenstone Road near the location, so we would like to speak to bus users as well as pedestrians and motorists.
"We have already carried out extensive inquiries with people who live close to the area."
Contact Det Sgt Holden on 101 or Crimestoppers on 0800 555 111.
