Police in the Norwegian capital of Oslo said they neutralised an explosive device found in a busy area of downtown Oslo and said they had arrested a suspect.
Norway was put on high alert after neighbouring Sweden suffered a truck attack in the capital that killed four people and injured 15.
Police Chief Vidar Pedersen confirmed that the Oslo device, initially described as "bomb-like," was an explosive. The police Twitter account said it had been defused or neutralised.
Police would not give any details about the suspect, or further information about the device.
Pedersen said the device was found on the street just outside the Groenland underground station, and police swept through the area to remove people from bars and restaurants.
"Every restaurant was being closed," said 23-year-old Malin Myrvold, who witnessed the scene from a fourth-storey window. "You could see cops in heavy armour going in every store and restaurant. We were trying to see what was going on. The police were screaming at us to get back inside and stay where we were."
The suspect in Saturday's attack in Sweden, a 39-year-old native of Uzbekistan, has been arrested. It was unclear whether he was also a Swedish citizen or resident or even how long he'd been in the country.
The brutal attack by a man who drove a stolen truck into shoppers in Stockholm has brought Sweden's open-door immigration policies under increased scrutiny - and raised the question if Swedish society, considered democratic and egalitarian, has failed to integrate its newcomers.
The suspect had been on authorities' radar previously but they dismissed him as a "marginal character".
Hundreds gathered at the site of the crash in the Swedish capital, building a heartbreaking wall of flowers on the aluminium fence put up to keep them away from the site's broken glass and twisted metal. Some hugged police officers nearby.
A girl of 11 is feared to be among the people killed.
The schoolgirl's desperate relatives appealed for help to find her after she failed to return home from school. "No one knows anything, she is just missing," said one relative.
The youngster often enjoyed passing the shops on her way home from school, they said. "She usually travels at that time, and that is a natural place for her to be," one relative added.
Swedish police took DNA from her home to help identify any remains found at the Stockholm's Queen Street shopping area, where the truck ploughed through a shop window before bursting into flames.
One survivor, grandmother Papusa Ciuraru, 83, spoke of the kindness of strangers who carried her to a hotel for treatment. She has undergone surgery in St Gran's Hospital after her leg was crushed under a concrete bollard.
"When I was laid there I thought - it was over," she told Swedish media. "People around me just screamed, I thought there was a war going on. I tried to pick myself up and run, but there was a large stone over my leg.
"Two people came up to me, one had a bike, but just left it to one side. They picked me up and carried me to Htorget and took me into a hotel where I received treatment. I was surprised and they stayed to help me. I thought that everyone would run past me and save themselves."
The driver appeared to target children as the hijacked lorry zigzagged along the pedestrianised street. Witnesses reported seeing children's buggies "flying through the air".
"It swerved from side to side. It didn't look out of control, it was trying to hit people," said tourist Glen Foran. "It hit people, it was terrible. It hit a pram with a kid in it, demolished it."
Television footage showed hundreds of shoppers and office workers fleeing the scene after the lorry careered down the precinct, killing a dog and crushing flowerpots and litter bins as it went.
"We stood inside a shoe store and heard something and then people started to scream. I looked out of the store and saw a big truck," Jan Granroth told the Aftonbladet newspaper.
Faisal Khan, whose brother and other family members died in a terror attack in Kabul three years ago, was on his way to buy a dozen roses to put on his sister-in-law's for her birthday. "I heard a loud noise followed by men and women screaming," he said.
"Luckily he was not a good driver. It felt to me like he did not have experience driving such a large vehicle. This guy -really wanted to cause a lot of damage." Omar Mirza was working in a shop as the truck stuck and said he saw a woman die in a man's arms.
Therese Walther, 30, was in the clothes store Zara when she saw the truck hit a girl. "It was coming as fast as hell. It ran straight over a girl." She said that Zara staff led her and dozens of others to its cellar for safety and locked the doors behind them.
Sweden has long been known for its open-door policy toward migrants and refugees. But after the Scandinavian country of 10 million took in a record 163,000 refugees in 2015 - the highest per-capita rate in Europe - Prime Minister Stefan Lofven conceded it could no longer cope with the influx.
At a press conference in late 2015, deputy prime minister of the small Greens Party - a junior government partner - Asa Romson, broke into tears as she announced measures to deter asylum-seekers in a reversal of Sweden's welcoming policy. She described it as "a terrible decision", admitting the proposals would make life even more precarious for refugees.
Lofven laid flowers at the truck crash site, declaring today a national day of mourning.
- Telegraph Group Ltd, AP