"A person has been arrested... I have been informed that he is a Norwegian," Storberget told a press conference yesterday.
"It would not be fair of me to go into more detail about this," he added.Storberget said the city centre blast had killed seven people and about 10 people had been seriously wounded.
Of the shootings at a youth camp held by the ruling Labour Party on the island of Utoeya, he said: "Several of our young people are dead and several others are missing."
Police arrested a man wearing a pullover with a police symbol on it on the island and believe he was involved in both attacks.
The suspect had never worked for the police, said Sveinung Sponheim, acting commissioner for the Oslo police.
So far, officers have put the death toll from the shootings at "nine to 10" people but have warned that that figure could rise.
Witnesses to the shootings described the gunman as Northern European-looking and said he spoke Norwegian.
"It is too early to say what is behind this," Prime Minister Jens Stoltenberg said during a joint press conference with his justice minister.
"The answer to violence is more democracy, more humanity, but not more naivety."You will not destroy us. We are a small nation, but a proud nation. No one will reduce us to silence us with bombs. No one will stop Norway from being itself," he added.