Swedish police on Monday tightened security near Jewish sites following a fire attack on a synagogue at the weekend, which came in the wake of the U.S. recognition of Jerusalem as Israel’s capital.

Masked assailants in Sweden’s second largest city, Gothenburg, hurled burning objects late Saturday at a synagogue where people were inside for an event.

The building did not catch fire and no one was hurt, but authorities took the incident seriously as it came days after U.S. President Donald Trump recognised Jerusalem as the Jewish state’s capital.

Mr. Trump’s announcements drew international condemnations and and sparked angry protests in the Middle East.

Authorities have not revealed the attack’s motive.

Police said they have detained three men on suspicion of attempted arson and prosecutors have until Wednesday to decide whether to extend their detention.

A police vehicle was parked on Monday near the Great Synagogue located in the heart of Stockholm, according to an AFP reporter at the scene.

Authorities have also boosted security for places of worship in Gothenburg and in the third largest city of Malmo, according to the official council of Swedish Jewish communities.

Malmo synagogue rabbi Moshe-David HaCohen on Sunday received Imam Sheikh Maher, a Muslim leader in Sweden.

“We do not accept any form of anti-Semitism or aggression against Jews in Malmo, in the same way that we do not accept any form of racism or discrimination,” the two men said in a joint statement.

Sweden’s Prime Minister Stefan Lofven also condemned the attack on the synagogue and “calls for violence against Jews.”

“There is no place for anti-Semitism in Swedish society,” he said in a statement.

The Swedish intelligence service SAPO has identified three militant movements hostile to the Jewish community: neo-Nazis, Islamists advocating violence, and some pro-Palestinian left-wing groups.

Gothenburg public prosecutor Stina Lundqvist told TT news agency on Monday that “there is no indication (the attack on the synagogue) is linked to the extreme right movement.”

“Gothenburg churches have been burnt down and mosques have been attacked all over Sweden, which shows that events abroad can quickly spill over,” the Gothenburg police chief told TT.