Following a tip-off, police found two unknown objects in the vicinity of the Arboga accommodation.
“Late on Friday night they found the first object and the second some time after midnight,” said Thomas Gustafsson, police spokesman in Västmanland.
A large area was cordoned off and bomb technicians from Stockholm were called.
“As a precaution it was decided that the accommodation would be evacuated,” Gustafsson told the Swedish TT news agency.
Staff from the Swedish Migration Board (Migrationsverket) and Arboga municipality removed the 83 residents and took them to a local church.
Bomb technicians found that the objects consisted of two sacks of flammable liquid. Police have launched a preliminary investigation.
Passers-by managed to extinguish the fire at a separate centre in Värnamo before the emergency services arrived. Twenty children and young people, between the ages of 15 to 21, were living there. Nobody was hurt.
“It was a resourceful intervention by passers-by that ensured the fire was stopped early,” said a police spokesman.
“We have undertaken an investigation and can conclude that the fire was not an accident. It has been classified as arson although we do not yet have any suspects.”
The attacks come just five days after a mother and her adult son were stabbed to death at an Ikea store in the central town of Västerås. Two men from Eritrea were arrested with one admitting the attack and another denying all involvement.
Story continues below…
Earlier this month two EU migrants were injured and four caravans burned when a camping site in Gothenburg was attacked.
Violence against ethnic minorities is growing in Sweden with other high profile cases in recent months including shots fired at two homeless EU migrants sleeping in a car in Boden in northern Sweden and two migrants assaulted in central Stockholm by a passerby who threw acid at them.