Normally unarmed police have been ordered to carry their weapons on patrol.

"We are raising the threat level from moderate to high in Norway due to several factors, primarily the current escalation in the Middle East," PST spokesman Martin Bernsen told AFP.

"We have no information about any concrete or realistic plans aimed at carrying out terrorist acts on targets in Norway," he stressed.

Following the announcement, Norway's police directorate ordered the officers, normally unarmed on patrol, to carry their service weapons.

"In Norway, it's the threat against Jewish and Israeli targets that has increased further," Bernsen said.

"There are several Jewish holidays in October and some people could take advantage of that to stage an attack," he added.

In addition to armed patrols, the police said it planned to bolster preventive measures, including boosting its presence at sensitive sites or gatherings and increasing border controls and surveillance.

According to Norwegian authorities, there are about 1,500 people in Norway's Jewish community, most of them in the Oslo area.

Israel's embassies in Denmark and Sweden were last week targeted in separate attacks, in Stockholm with explosions in its vicinity and gunfire in Copenhagen.