ISIS Claiming Responsibility For Deadly Truck Attack At Berlin Christmas Market

BERLIN (CBS) -- The Islamic State of Iraq and Syria is claiming responsibility for the truck attack on a Berlin Christmas market that killed 12 people and left nearly 50 injured.

German police are still searching for the driver of the truck, after a man held for questioning was released for lack of evidence.

German Chancellor Angela Merkel visited the site Tuesday where the deadly attack took place. Investigators are treating the incident as an act of terrorism.

Police initially detained an asylum seeker from Pakistan, but he denied any involvement and was released because of insufficient evidence. Authorities said they cannot rule out the possibility a suspect is on the loose.

"The ambulances, they come quick, and we had to close all the shops quickly, so quickly that I could not close," one shop owner said.

A Polish driver was supposed to be using the truck to deliver steel beams. That man was found fatally shot and stabbed inside the cab.

After the truck attack, police in London are taking new precautions. For the next three months roads will be closed outside Buckingham Palace during the changing of the guard.

President Barack Obama spoke with Merkel Monday night to offer his condolences and assistance.

President-elect Donald Trump said he is "closely monitoring" the aftermath of the attack.