A suspected right-wing Christian gunman in police uniform killed at least 84 people in an attack on a youth summer camp of Norway's ruling Labour party, hours after a bomb killed seven in Oslo.
Here is a snapshot timeline of some of the worst shooting incidents carried out by one or two gunmen around the world in the last 20 years:
April 1982 - South Korea - Police officer Woo Bum Kong went on a drunken rampage in Sang-Namdo with rifles and hand grenades, killing 57 people and wounding 38 before blowing himself up.
Aug. 19, 1987 - Britain - Michael Ryan, a 27-year-old gun fanatic rampaged through the English town of Hungerford, killing 16 people and wounding 11 before shooting himself.
July 1989 - France - A French farmer shot and killed 14 people including members of his family in the village of Luxiol, near the Swiss border. He was wounded and captured by police.
Dec. 1989 - Canada - A 25-year-old war movie fan with a grudge against women shot dead 14 young women at the University of Montreal, then killed himself.
Nov. 1990 - New Zealand- A gun-mad loner killed 11 men, women and children in a 24-hour rampage in the tiny New Zealand seaside village of Aramoana. He was killed by police.
Sept. 1995 - France - A 16-year-old youth ran amok with a rifle in the town of Cuers, killing 16 people and then himself after an argument with his parents.
March 13, 1996 - Britain - Gunman Thomas Hamilton burst into a primary school in the Scottish town of Dunblane and shot dead 16 children and their teacher before killing himself.
April 1999 - USA - Two heavily-armed teenagers went on a rampage at Columbine High School in Littleton, Denver, shooting 13 students and staff before taking their own lives.
July 1999 - USA - A gunman killed nine people at two brokerages in Atlanta, after apparently killing his wife and two children. He committed suicide five hours later.
June 2001 - Nepal - Eight members of the Nepalese Royal family were killed in a palace massacre by Crown Prince Dipendra who later turned a gun on himself and died few days later. His youngest brother also died later raising the death toll to 10.
April 26, 2002 - Germany - In Erfurt, eastern Germany, 19-year-old Robert Steinhauser opened fire after saying he was not going to take a maths test. He killed 12 teachers, a secretary, two pupils and a policeman at the Gutenberg Gymnasium, before killing himself.
Oct. 2002 - USA - John Muhammad and Lee Malvo killed 10 people in sniper-style shooting deaths that terrorized the Washington, D.C., area.
April 16, 2007 - USA - Virginia Tech, a university in Blacksburg, Virginia, became the site of the deadliest rampage in U.S. history when a gunman killed 32 people and himself.
Nov. 7, 2007 - Finland - Pekka-Eric Auvinen killed six fellow students, the school nurse and the principal and himself with a handgun at the Jokela High School near Helsinki.
Sept. 23, 2008 - Finland - Student Matti Saari opened fire in a vocational school in Kauhajoki in northwest Finland, killing nine other students and one male staff member before killing himself.
March 11, 2009 - Germany - A 17-year-old gunman dressed in black combat gear killed nine students and three teachers at a school near Stuttgart. He also killed one other person at a nearby clinic. He was later killed in a shoot-out with police. Two additional passers-by were killed and two policemen seriously injured, bringing the death toll to 16 including the gunman.
June 2, 2010 - Britain - Gunman Derrick Bird opened fire on people in towns across the rural county of Cumbria. Twelve people were killed and 11 injured. Bird also killed himself.
Aug. 30, 2010 - Slovakia- A gunman shot dead six members of a Roma family and another woman in the Slovak capital Bratislava before killing himself. Fourteen more people were wounded.
July 22, 2011 - Norway - Police seize a gunman, identified as a 32-year-old Norwegian, who killed at least 84 people at a youth summer camp of Norway's ruling political party, on the small, holiday island of Utoeya. Anders Behring Breivik is later charged with the killings, as well as with an earlier bombing in the centre of Oslo which killed at least seven people.