State Secretary Raymond Johansen told Aftenposten.no that the Norwegian government was adamantly opposed to the execution of Rahele Zamani, the 27-year-old mother of two young children.
Zamani had been convicted of murdering her husband. She claimed he had abused her for years. The couple had two children, a three-year-old boy and a five-year-old girl.
"It's just terrible that these two children must now grow up without a mother or father," Johansen said.
"We will now contact Iran's ambassador (to Norway) and protest this barbaric act."
The execution of Zamani was carried out in the Evin Prison in Teheran, according to the human rights organization Iran Human Rights. She was reportedly hanged at the prison.
The execution was also confirmed by the Norwegian authorities' sources in Teheran.
Johansen said Norway can't allow itself to believe that it alone can influence a large country like Iran, but its formal protest was "important for the internal opponents of the death sentence in Iran."
He said western countries' use of the death sentence, like the US, also undermines international campaigns against executions.
Norway has also lodged formal protests against earlier executions in Iran, and took up the issue with Iran's foreign minister when he visited Norway last May.