Two teenagers have been arrested by Swedish police for throwing percussion caps at a Jewish community centre and raising fears of a racial attack.
The incident happened in Sweden's third largest city, Malmo, where a series of hate crimes against Jews has been reported since Israel's invasion of Gaza in 2009.
Two 18-year-old men were being questioned by police on suspicion of vandalism. They were stopped in a vehicle leaving the area but denied any involvement in the incident.
The small blast damaged windows at the community centre which is home to a kindergarten, meeting halls and apartments.
Police said the percussion caps would not have posed any danger.
But jewish leaders said the incident was another example pf growing anti-semitism.
"Jewish institutions in Sweden are under constant threat," Fred Kahn, president of the Jewish Community in Malmo, told the TT news agency.
"You don't wear a kippah [Jewish skullcap] in this city. That would be suicide," the head of Malmo's voluntary security team guarding the gates of the city's Jewish cemetery told the Jewish Chronicle Online.
According to Israel newspaper Haaretz, Malmo's rabbi, Shneur Kesselman, said he had had personal experience of some 90 anti-semitic incidents in the last seven years.
Malmo, which is home to about 600 Jews, has a large immigrant Muslim community, many of whom are said to be of Palestinian origin.
The Swedish government earmarked 4 million Swedish Kronor (£400,000) to increase security for the Jewish minority.