Norway closed part of the airspace over its second city Bergen and tightened border checks on Saturday, two days after the country upped security following what it described as a "terror alert".
Norway has been on high alert since Thursday, when its intelligence service (PST) said it had "recently received information that a group of fighters from Syria may be planning a terrorist attack" in the country.
"Police have requested Avinor (Norway's state-owned airport operator) to ban flights over central Bergen," said Gustav Landro, chief of staff at the Hordaland county police department.
"The reason is the increased threat situation we have had since Thursday," he added.
Police said the airspace ban applied only to smaller private and recreational flights over the centre of the city in Western Norway.
"Non-specific" but "credible" threat
Bergen's airport was not disrupted and was operating normally, police said.
On Saturday, authorities said they would check the ID of all travellers entering Norway until further notice.
Norway is not an EU member but is part of the Schengen area, which includes 26 European countries that have abolished passport and other types of border controls for people travelling within the group of nations.
At a press conference on Friday, Odd Reidar Humlegaard, head of the police directorate, said any security incident was unlikely.
"But this time around, we will be more prepared than ever to handle the situation if it occurs," he added in an implicit reference to the massacre by right-wing extremist Anders Behring Breivik, who killed 77 people in July 2011, when police were heavily criticised for their slow reaction.
The threat is "non-specific" but "credible", according to PST chief Benedicte Bjoernland.
On Friday, the Oslo Jewish Museum in Norway announced it would remain closed to the public until Sunday.
There were concerns Norway's Jewish community could be targeted following an attack on Brussels' Jewish Museum in May.