OSLO, Norway—Norway's chief of police has stepped down following scathing criticism of the police's bungled response to a bomb and gun massacre that left 77 dead last year.

In a statement Friday, Oystein Maeland said he had quit his job with immediate effect because he felt he no longer had the backing of the government.

The announcement came four days after a government-ordered report into the twin attacks of July 22, 2011, said police could have stopped the gunman earlier.

After setting off a bomb in Oslo, confessed killer Anders Behring Breivik went on a shooting rampage at a summer camp for youth for more than an hour before police arrested him.

The self-styled anti-Muslim militant is awaiting sentencing Aug. 24.