STOCKHOLM (The Blaze/AP) -- Swedish police arrested four people on suspicion of preparing a terror attack and evacuated an arts center in the country's second largest city, security officials said Sunday.
The four were arrested in the west coast city of Goteborg and were suspected of plotting terrorism, security service spokeswoman Sara Kvarnstrom said. She declined to give details on the arrests and wouldn't say whether they were linked to the 10th anniversary of the Sept. 11 attacks.
Kvarnstrom said Swedish security service SAPO saw no reason to raise its terror alert level, which has been at "elevated" since October.
"Our assessment is that there is no reason for public concern at the moment," she told The Associated Press.
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Swedish tabloid Expressen, citing an unnamed police source, said investigators suspect the men belong to a terror network with links to al-Qaida, and that they had acquired, or were trying to acquire, firearms, explosives and hand grenades. Security police declined to comment on the newspaper's information.
Police in Goteborg said in a statement they had evacuated the Roda Sten arts center, located beneath the city's landmark half-mile (930-meter) Alvsborg bridge, because of a threat deemed to pose "serious danger to life, health or substantial damage of property."
Kvarnstrom declined to say if the arts center or the bridge were considered potential targets for a terror attack.
The Alvsborg bridge runs over Goteborg's harbor to connect the mainland with the island of Hisingen. The six-lane passage is a vital link from the Norwegian capital Oslo to southern Sweden.
Goteborg police and Sweden's Stockholm-based counterterrorism unit assisted security police with the arrests.
Henrik Wallgren, 46, says he saw a Swedish navy combat boat race back and forth on the river by the arts center just before he and others were evacuated from the center.
"We were sitting on a skateboard ramp behind the graffiti wall at Roda Sten," when it happened, he told The Associated Press.
Roda Sten is a former heating plant that was abandoned for years before being reopened as an arts center in 2000, according to its website. About 400 people were celebrating the opening of an international biennial for contemporary art at the graffiti-covered brick building when police ordered everyone to leave, said Mia Christersdotter Norman, the head of Roda Sten.
"Around midnight I was called out by the police and they said there was a threat to the building and asked us to quietly stop the party, which we did and everyone left," Christersdotter Norman told The Associated Press.
"Police have searched the building but they didn't find anything," she said, adding the arts center would reopen as usual Sunday.
She said she had no information about the arrests, and had not been aware of any threats against the arts festival or its participants before the police operation.
Klas Eriksson, a DJ, was just about to start playing at Roda Sten when police broke up the party. People were worried but there was no panic, he said.
"It was just after midnight. Police said that they had arrested four people and that the building had to be evacuated," Eriksson told AP.
"I thought it was scary," he said. "Your thoughts go to 9/11, because it was just after midnight. But you don't know. It could be anything."
In December, suicide bomber Taimour Abdulwahab blew himself up in downtown Stockholm among panicked Christmas shoppers, injuring two people and causing shock in a country that had largely been insulated from terrorism.
The 2007 drawing of the Prophet Muhammad by a Swedish cartoonist raised tensions in Sweden. In May, Lars Vilks was assaulted while giving a speech in Uppsala, and vandals unsuccessfully tried to burn down his home in southern Sweden. His cartoon was reportedly the inspiration for Abdulwahab's attack. Vilks was not attending the art biennial in Goteborg.
In a report detailing the extent of extremist Islamist networks in Sweden, ordered months before that attack, SAPO had downplayed the risk of terror attacks in the Nordic country. Activity among radicalized Muslims in Sweden is primarily directed toward supporting militants in other countries, including Somalia, Afghanistan and Pakistan, it said.
Magnus Norell, a terrorism expert at the Swedish Defense Research Agency, declined to speculate about what was behind the arrests, but said the general threat in Sweden remains low.
"It was low in December 2010 as well - but at the same time Sweden is a part of the world and a global context," he said.
Scandinavia has largely been focused on Islamic terrorism since Sept. 11, but in the wake of Norway's terrorist attack by a right-wing anti-immigrant Norwegian, the European police agency said it was setting up a task force of more than 50 experts to help investigate non-Islamist threats in Scandinavian countries.
The Swedish government said it would earmark 62 million kronor ($9.5 million) to set up a national action plan against all kinds of violent extremism, focused on prevention.