Norway's PM said she was "sad and furious" about the vandalism.
ADVERTISEMENTThe memorial to a victim of a racist murder in Norway has been vandalised, just days before the country commemorates victims of far-right attacks in 2011.
Police in Oslo have launched an investigation after a statue of Benjamin Hermansen was damaged.
Hermansen, a Norwegian-Ghanaian boy, was murdered by three members of the neo-Nazi group in a racially motivated attack in 2001.
A memorial to the 15-year-old in Holmlia, near the capital city Oslo, was tagged with the words "Breivik was right", a reference to the perpetrator of the 2011 attacks.
On Thursday, Norway will pay tribute to the 77 victims who died when Anders Behring Breivik committed a bomb attack in the Norwegian capital and mass shooting at an AUF youth camp on Utøya island.
The vandalism on the statue of Hermansen was discovered on Tuesday by Johannes Dvorak Lagos while on a walk near his home.
Lagos posted an image of the graffiti on Twitter, describing it as a "reprehensible" act.
The damage has also been condemned by Norway's Prime Minister Erna Solberg and opposition Labour leader Jonas Gahr Støre.
"It is absolutely awful to see that the Benjamin Hermansen memorial at Holmlia has been tagged down just before 22 July," Solberg said on Twitter.
"I am sad and furious, and this shows how important it is that we stand up against racism and hate speech every single day."
"It's reprehensible and it shows that dangerous attitudes are still circulating," Støre added on Twitter.
"The police must take it seriously, and together we must speak out against this."
Authorities say they are investigating the matter as a potential hate crime and added that the graffiti had been removed on Tuesday afternoon.
"The police take this seriously," said a spokesperson for the Oslo department, Marthe Kvalsvik Rørstad.
"A case has been opened for serious damage with a motive of hatred ... The case has been transferred to the hate crime group for further investigation."
Meanwhile, Norwegian police also arrested four people on Tuesday as part of an ongoing investigation into right-wing extremism.
Authorities detained one man and seized dozens of weapons during a raid in Bodø, while two others from Lillestrøm and Hamar were also arrested.