The police district responsible for the case confirmed to broadcaster NRK that it would now look at the report in order to assess whether investigative proceedings should be set in motion, the broadcaster writes.
The report relates to the accusation that Riise, 29, had sex with a 16-year-old girl when she was highly intoxicated.
Riise left his position as leader of the Young Conservatives on January 10th after reports of the incident emerged in Norwegian media.
Following considerable coverage in the Norwegian press since then, the state prosecutor has asked police to look into the complaints made against Riise, according to NRK.
Newspaper Aftenposten originally reported earlier this month that Riise had sex with a heavily intoxicated 16-year-old at a Conservative (Høyre) party regional annual meeting in 2014, when he was 25. The girl told Aftenposten that she did not want to have sex with Riise but was very drunk and remembers little of what happened.
Riise later said in a text message sent to news agency NTB that was "positive towards this issue being clarified thoroughly and objectively. I have previously confirmed that we had sex and had both drunk alcohol, and apologise sincerely. Apart from that I do not agree with the version of events as represented in the media".
Police in the relevant district confirmed to NRK on Wednesday that they had begun initial investigation and delegation of tasks. A recommendation on whether to set in motion a full investigation will later be presented to the state prosecutor, the broadcaster writes.
The former Young Conservatives leader has previously said that he did not wish to take part in a public discussion of the incident. His lawyer Finn Krokeide told NRK via SMS on Wednesday that he had no further comment.