A 17-year-old asylum-seeker from Russia was arrested Sunday in connection with an explosive device found near a busy subway station in Norway's capital and defused before it detonated, authorities said.

The youth was detained on suspicion of handling explosives, but investigators do not know if he planned to carry out an attack with the homemade device, Signe Aaling, chief prosecutor for Norway's PST security service, said.

"PST is now working on finding his intentions and find out whether others are involved," Aaling said.

The youth was not identified, but security service head Benedicte Bjornland said intelligence agencies were aware of him. He is an asylum-seeker from Russia who arrived in Norway with his family in 2010, Bjornland said.

Bjornland also alleged that the youth was part of "extreme Islamism" circles in Norway.

"It is likely that that attacks in France, German, Great Britain, Russia and Sweden can create a copycat effect in Norway with people with Islamic sympathies," Bjornland said, listing of the locations of extremist attacks that have devastated Europe in the last year.

The discovery of the explosive Saturday night — found on the street just outside the Groenland subway station — prompted police to evacuate late bars and restaurants in the Norwegian capital.

The Oslo explosive was found less than a mile from the government buildings that were damaged in a deadly bomb attack carried out by right-wing extremist Anders Breivik in 2011. That bomb and a subsequent gun massacre at a Norwegian island killed a total of 77 people.

Norway was put on high alert after neighboring Sweden suffered a truck attack in Stockholm on Friday that killed four people and injured 15.

Norway intelligence agency raised the terror threat in the country on Sunday to "likely" for "a two-month period."