Saying "I apologize," Stoltenberg told a special session of the Norwegian Parliament Tuesday accepted a scathing report on the police response following a car bombing in Oslo that killed eight and the ensuing massacre of 69 young people by Anders Behring Breivik on July 22, 2011.
The report, issued by the July 22 Commission, came less than a week after Breivik was sentenced to 21 years in prison, with the possibility of a longer sentence if he continues to show a lack of remorse.
Stoltenberg told the Storting, he hadn't been prepared for the extent of the criticism in the commission's report, and acknowledged that it was hard to face up to such fundamental shortcomings given the magnitude of the tragedy.
"We can never correct mistakes of the past," the prime minister said. "But we can learn from the past, recognize that we made mistakes and do what we need to create a more secure future."
The commission found several main shortcomings with the government and police response to the attack, which began with a car bomb blast on the Grubbegata -- the street in front of Norway's main government buildings -- and concluded 2 1/2 hours later with Breivik's surrender to police after the killing of 69 attendees at Norwegian Labor Party's youth camp on the island of Utoya.
Among its criticisms, the commission found that the attack on the government building could have been prevented through effective implementation of already adopted measures and that a faster police action at Utoya was possible -- Breivik could have been stopped earlier in the day, it said.
Also, it found, more security and contingency measures to prevent new attacks and reduce the damage should have been implemented after the initial bombing.
And while there was no basis to conclude the Norwegian Police Security Service could have or should have prevented the attacks, with better working methods and a broader focus, security forces could have been on Brievik's trail before July 22.
On the positive side, the commission said health and emergency personnel efficiently tended to the injured and their families during the acute phase of the crisis and that the government was able to keep the public well-informed of the situation.
As for the causes of the shortcomings, the commission determined the problem wasn't that there were no emergency plans, but that they weren't implemented.
It also blamed an inability to learn enough from drills and a generally poor attitude and culture regarding emergency preparedness.
"The commission documents a decline in Norwegian preparedness and contingency culture that is more comprehensive and deeper than I was prepared for," Stoltenberg said. "It is hard to face up to."
But he promised "clear leadership" in correcting the errors.
"There should never be any doubt about the direction and goal," Stoltenberg said. "For me this is a major task -- one that I intend to solve."
Celebrity Couples of 2014 [PHOTOS]