Oslo's Pride march was called off on Saturday following deadly overnight shootings, including at a gay bar in the Norwegian capital.
"All events linked to Oslo Pride have been cancelled" following "clear" recommendations from police, the organisers of the march wrote on Facebook, as the Norwegian security service raised its terror alert to the highest level.
Police said they were investigating the shootings, which left two dead and at least 14 wounded, as a "terrorist attack".
The anti-terror service later said it was being treated as an "act of Islamist terrorism".
A suspect was arrested after the shootings, which occurred at around 1am (11pm GMT) in three locations, including a gay bar in Norway's capital.
The suspect is a Norwegian of Iranian descent, police said on Saturday, without naming him.
The man was known to domestic intelligence services and had had brushes with the law for minor infractions, including knife and drug possession, police said.
Police attorney Christian Hatlo said the suspect was being held on suspicion of murder, attempted murder and terrorism, based on the number of people targeted at multiple locations.
"Our overall assessment is that there are grounds to believe that he wanted to cause grave fear in the population," Hatlo said.
Public broadcaster NRK and other local media reported that the shooting took place at the London Pub, a popular gay bar and nightclub in the centre of the city.
"I saw a man arrive with a bag, he picked up a gun and started to shoot," NRK journalist Olav Roenneberg told the broadcaster's news website.
The crime scene extended from the London Pub via a neighbouring club and towards a nearby street where the suspect was apprehended a few minutes after the shooting began, police spokesman Tore Barstad told newspaper Aftenposten.
Oslo had been due to hold its annual Pride parade just hours after the attack took place.
"Two people are confirmed dead," the Oslo police department said in a tweet.
Fourteen people were taken to hospital, several with severe injuries, police said.
Oslo's university hospital said it had gone on red alert following the shooting.
Photographs published by newspaper VG, broadcaster NRK and others showed a large gathering of emergency responders outside the London Pub, including police and ambulance workers.
Helicopters hovered above central Oslo while ambulance and police car sirens were heard across the city.