Danish police arrested about 20 people on Wednesday after carrying out raids throughout the country to thwart what they suspected were preparations for an Islamist militant attack, police and security officials said.
The detainees had tried to obtain explosives and firearms, police said.
The raids were mounted on the suspicion that several people had been planning an attack, the Danish intelligence service said in a news conference with police.
"It is our assessment, that those people are driven by a militant, Islamist motive," operational chief of the intelligence service, Flemming Drejer, said.
Police did not give a precise number for the arrests.