The suspect used a long blade "similar to a machete," the police said on Monday.

According to the couple camping on the outskirts of Bonn, the man entered their tent early on Sunday and threatened them with his weapon in "broken English." He then forced the 23-year-old woman outside, raped her and fled the scene in the direction of the Rhine river.

The victim's 26-year-old boyfriend called the police. The authorities managed to secure multiple pieces of evidence and launched a manhunt for the suspect which included a helicopter and a sniffer dog team. Despite their efforts, however, the suspect remained on the loose.

On Monday, the police published a facial composite sketch of the assailant and asked the public to help them in the search. According to investigators, the suspect is a dark-skinned individual in his 20s, and around 180 centimeters (5 feet 11 inches) tall. At the time of the attack, he was wearing a light-colored pair of jeans and a short jacket.

Police were also investigating reported sightings near the crime scene.

The issue of migrants and sex crimes is an especially sensitive topic in this area of Germany, after the mass sexual assaults against women in the nearby city of Cologne during New Year celebrations on December 31, 2015.