HELSINKI -- Norway paid an emotional tribute Friday to the 77 people killed in a bombing-and-shooting rampage five years ago, with church services and other events marking what the prime minister called "one of the darkest days in Norwegian history."

Prime Minister Erna Solberg, Crown Prince Haakon and Crown Princess Mette-Marit laid wreaths at the government offices in the Norwegian capital, Oslo, where Anders Behring Breivik exploded a car bomb that killed eight people before driving to the island of Utoya where he gunned down 69 people -- mostly teenagers -- at a youth summer camp.

Later they attended a memorial service at Oslo Cathedral, which also included victims' families, friends and representatives of a left-wing youth group that hosted the camp on Utoya.

"We still see traces of the terrorist acts. The missed ones will always be there. Time does not heal all wounds," Solberg said at the memorial ceremony, where the names of all those killed were read out. "The biggest impact is felt inside us as human beings."

In 2012, Breivik was convicted of mass murder and terrorism and given a 21-year prison sentence that can be extended for as long as he's deemed dangerous to society. Legal experts say he will likely be locked up for life.

His attacks traumatized the nation of 5 million, where an estimated one in four people were affected through connections with family, friends or acquaintances of the victims.

NATO Secretary-General Jens Stoltenberg, Norway's prime minister at the time, said he had painful memories of that fateful day -- July 22, 2011.

"It hurts to hear all the names read out," Stoltenberg said. "But it's also good to be with other people who were affected that day, and we give each other support and comfort."

In the afternoon, a ceremony was held on Utoya, a small island on a lake surrounded by wooded hills, 40 kilometres (25 miles) northwest of Oslo. It reopened to the public a year ago, when 1,000 youth organization students enrolled for a camp held in memory of the victims.