"The violent incidents in our streets must be stopped. It is completely unacceptable," Frederiksen told Ritzau news agency on Saturday.
"This is not the Denmark that we want," she added, Xinhua reported.
To combat the rising violence, Frederiksen urged police to crack down on gangs and their activities.
On Friday, Denmark escalated border controls with Sweden due to the growing involvement of Swedish criminals in activities in Copenhagen.
Justice Minister Peter Hummelgaard said that the situation had become so critical that Danish police would "significantly increase controls at the border."
The enhanced measures include more rigorous physical checks on cross-border trains and the deployment of additional cameras to scan license plates at border crossings between Denmark and Sweden.