Kim Hjelmgaard

USA TODAY

BERLIN — The Islamic State claimed responsibility Tuesday for the truck rampage through a crowded Christmas market here, as German authorities released a suspect for insufficient evidence in the attack that killed 12 people and injured 48.

“We may still have a dangerous criminal out there,” Berlin police chief Klaus Kandt said in acknowledging that the driver of the truck was still at large.

The detained suspect, a Pakistani who arrived in Germany last year, denied involvement in Monday's attack, and no forensic evidence showed he was in the cab of the truck.

The Islamic State called the attacker a "soldier" of the militant group, its Amaq News Agency reported.

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Police urged people to remain vigilant and report any suspicious activity to a special hotline.

German Chancellor Angela Merkel called the incident an "assumed terror attack."

Merkel and German President Joachim Gauck attended a memorial service Tuesday at the Kaiser Wilhelm Memorial Church, near the deadly scene, and laid white roses outside the church.

Merkel also spoke with the leaders of France, Turkey, Italy, Greece, Poland, Sweden and Spain, who expressed their support to investigate the attack and “stressed the necessity of European solidarity in the fight against terrorism,” a government statement said.

In Washington, State Department spokesman John Kirby said the attack “bears the hallmarks of previous terror attacks,” but U.S. officials didn’t have enough information to back up the Islamic State's claim of responsibility. “There is no direct evidence of a tie or a link to a terrorist organization,” he said.

Six of those killed were identified as Germans, and a man found shot and killed in the truck’s passenger seat was Polish. The other five people killed have not yet been identified, the Associated Press reported.

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The attack resembles the July 14 assault in Nice, France, when a truck slammed into people celebrating Bastille Day, killing 86. Berlin joins the European capitals of Brussels and Paris that have had recent attacks. And Merkel will face renewed scrutiny of her decision to allow almost 1 million asylum seekers to enter Germany last year, a move that already brought her heavy criticism.

"Under the cloak of helping people Merkel has surrendered our domestic security,” Frauke Petry of the far-right Alternative for Germany party, wrote on Facebook.

Merkel earlier said it would be particularly troubling if the attacker turned out to be an asylum seeker. "This would be especially despicable toward the many Germans who are daily engaged in helping refugees, and toward the many people who truly need this protection," she said Tuesday at a news conference.

A witness to Monday night's attack, Trisha O'Neill from Australia, said, "I saw this huge black truck speeding through the markets crushing so many people and then all the lights went out and everything was destroyed." She told the Australian Broadcasting Corporation: "I could hear screaming and then we all froze."

Investigators believe the truck, which was carrying steel beams, was stolen in Poland. It has Polish license plates and a man found dead in the passenger seat was a Polish national. Police said the dead passenger may have been the truck's original driver, and the truck's owner said he feared the vehicle could have been hijacked.

The Polish victim was identified as Lukasz Urban, 37.

"I believe he would not give up the vehicle and would defend it to the end if were attacked," Lukasz Wasik, the manager of the trucking company where Urban worked, told Poland’s state broadcaster TVP.

The attack comes while Europe has been on high alert for terrorist attacks inspired or coordinated by the Islamic State. Since July, Germany has experienced a number of small-scale attacks by Islamic militants who have used guns, axes and bombs, but no mass casualties. A few weeks ago, a 12-year-old with dual German-Iraqi citizenship failed to detonate a nail bomb at a Christmas market in Ludwigshafen, a city in western Germany.

"Whatever we find out going forward about the exact background motive of the perpetrators, we must not and will not allow our free life to be taken away," Interior Minister Thomas de Maiziere said.

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