"Someone threw a firebomb, a Molotov cocktail, at the [mosque] building," Uppsala police spokesman Torsten Hemlin told Swedish news agency TT Thursday, adding that the vandals also "wrote some vulgar, racist words".
According to Hemlin, there were no people in the mosque at the time of the attack. Police are still searching for the culprit.
On December 29 a mosque was damaged by fire in the southern Swedish town of Eslov, located north of Malmo. No one was injured in the suspected arson attack.
On Christmas Day, an arsonist attacked a mosque in the Swedish town of Eskilstuna. The fire injured five people.
After the Eskilstuna incident, government officials urged Swedes to reject xenophobia and protect religious freedom.