There had been speculation in advance that the Prime Minister would make his announcement during Tuesday's opening of the Folketing.
That was not the case.
To the journalists' questions afterwards, Frederiksen replied cryptically that "an election will be held".
The background to the demands for new elections is the mink scandal that rocked Denmark during the corona pandemic.
The investigation into the incident has caused the support party Radikale Venstre to issue an ultimatum: call new elections by Thursday at the latest, otherwise there will be a vote of no confidence.
The Danish electoral system differs from the Swedish one.
In the neighboring country, it is the Prime Minister who decides when it is time for an election, as long as it takes place no later than four years after the last election.
Follow Mette Frederiksen's press conference in the player above.