“It is PET’s opinion that with the arrests we have avoided a concrete act of terror,” PET said in a statement.
The two brothers, aged 18 and 23, whose names were not given, were arrested on Monday — one at his home in the central city of Aarhus and the other as he arrived by plane at Copenhagen airport, it said.
“The arrested are suspected of having been in the process of preparing an act of terror, among other things through conversations about methods, targets and the use of weapon types,” it said.
“One of the arrested is also suspected of having undergone training, instruction and teaching at an al-Shebab training camp in Somalia with the aim of carrying out an act of terror.”
Police had conducted searches at two separate addresses in Aarhus in connection with the arrests.
Both men held Danish citizenship and had been living in the Aarhus area for the past 16 years, PET said, adding they would go before a judge on Tuesday to determine whether they will be remanded in custody.
Since the attack the brothers are suspected of planning was averted, PET said there was no need to raise the terror threat level in Denmark, which is nonetheless considered “serious”.
The arrests came just over a month after Danish police arrested three people in Copenhagen, also suspected of planning a “terrorist act”.
They also come as four others remain on trial for allegedly plotting to massacre the staff of a Danish newspaper, Jyllands-Posten, which first published 12 controversial cartoons of the Prophet Mohammed in 2005 that triggered violent and sometimes deadly protests around the world.
Jyllands-Posten and the cartoonist who drew the most controversial of the caricatures, Kurt Westergaard, have been the targets of a string of attempted and plotted attacks in recent years.