Acting police chief Roger Andresen told the NTB newswire that the decision to arm police was intended to boost confidence in the wake of Tuesday morning's terror attack in Brussels.
“We have introduced temporary arming of all patrols carried out by the Oslo police,” said acting police chief Roger Andresen.
“This is because of he unresolved situation in Belgium, both in terms of the scope of the attack and in who is behind it.”
At least 13 people were killed in the explosions at the airport, according to the latest reports in Belgian media, and several dozens have been left injured.
Metro operator Stib confirmed 15 casualties in the metro blast and 55 wounded, however unconfirmed police reports claimed the death toll could rise.
The Belgian prosecutor said that the airport explosions were suicide bombings, confirming the fears that the capital was targeted by terrorists.
Foreign Minister Børge Brende called on Norwegians to show solidarity with Brussels.
“We must stand together,” he said.” This is the capital of Europe. It is democracy.”
As yet, he said, there had been no reports of Norwegian casualties.
Meanwhile, Norway's King Harald sent a message of condolence to King Philip of Belgium.
“I have with great sadness received the news of the heinous attacks today in Brussels which resulted in many deaths and injuries,” he wrote.
From November 2014 until the end of this January, Norwegian police carried their service weapons in their belts on the recommendation of the Norwegian Police Security Service (PST), which feared an imminent terror attack.
At the end of January, a decision was made to go back to keeping arms locked within police vehicles.