ISIS claims credit for Christmas market attack in Berlin

The terrorist group ISIS claimed credit on Tuesday for an attack the previous day on a Berlin Christmas market that killed 12 people and injured dozens.

The claim was published by Amaq News Agency, the unofficial propaganda news arm of ISIS.

Amaq referred to the attacker, who drove a truck into the market outside the Kaiser Wilhelm Memorial Church, as a "solider" of ISIS.

The truck apparently belonged to a Polish transportation company and was loaded with metal rods.

German investigators have been treating the attack as an act of terrorism. The White House on Monday called it a terrorist attack, and Merkel said German authorities were investigating under the assumption that terrorism was involved.

German police have one suspect in custody, but it is unclear whether he was the truck driver.

It's unclear whether the attacker or attackers coordinated with ISIS leadership or carried out the attack on their own.

Terrorist groups have long been urging supporters to attack "infidels" with cars. Vehicles were used in attacks at Ohio State University in the US late last month and in Nice, France, in July.

Amaq's statement notes the attack was "in response to appeals to target nationals of the international coalition" fighting ISIS.

Natasha Bertrand contributed to this report.