UPDATE 2 - Germany: Christmas market incident was probable attack

UPDATES WITH REMARKS BY GERMAN FEDERAL PROSECUTOR, OBAMA CALL WITH MERKEL

By Ayhan Simsek

BERLIN (AA) - German authorities have announced that those responsible for Monday’s deadly truck attack on a Berlin Christmas market could still be at large, as the police went on high alert and further reinforced presence at public places.

Germany’s top federal prosecutor Peter Frank has confirmed Tuesday that the only suspect under arrest might not be the perpetrator who drove the truck through the crowds at a Christmas market, killing at least 12 and injuring nearly 50 others.

“For the time being, we still do not know with certainty, whether there was one perpetrator or more,” he told a press conference in Berlin.

“We must also get used to the idea that, at the end of the investigation, it might be clear that the suspect who was temporarily arrested last night, who is a citizen of Pakistan, may not have been the perpetrator or belong to the group of perpetrators,” he added.

Frank underlined that authorities were investigating a suspected terror attack, as the indications show that the truck was intentionally steered into the crowd in the Christmas market.

On Monday night, witnesses told local media that the driver ran away from the truck soon after the incident. The truck had a Polish license plate.

Police have found the dead body of a Polish citizen in the truck, and said he is believed to have been killed by the suspect or suspects who had stolen the truck.

- Merkel promises full investigation

Chancellor Angela Merkel has expressed shock and deep sorrow on Tuesday for the deadly attack, but also vowed that Germany will not bow to terrorism.

“We still don't know many details with certainty, but at this stage we have to presume that this was a terrorist attack,” Merkel told reporters.

She stressed the German government would take all necessary measures, but not let terrorists force the public to change their lifestyle.

“We will find the strength to live our lives in Germany the way we want it -- free, together and open,” she said.

Merkel promised a full investigation into the incident and said those involved would be punished using the full strength of the law.

- Obama called Merkel

During a Monday night call with Merkel, U.S. President Barack Obama expressed condolences "for the horrific apparent terrorist attack," the White House said.

Obama further restated the U.S. offer to assist German officials as they investigate the tragedy "and underscored that no attack could sway our determination--and that of our German allies--to defeat terrorism in all of its forms."

"The President expressed his appreciation for Chancellor Merkel's steadfast leadership in our shared efforts to root out the scourge of terrorism and defend our way of life," the White House said in a Tuesday readout of the call.

- Christmas markets closed on Tuesday

Authorities in Berlin demanded the closure of Christmas markets on Tuesday, to demonstrate respect for the victims of the suspected attack.

Federal Interior Minister Thomas de Maiziere underlined that Christmas markets in Berlin and across Germany will remain open in the coming days.

“We are not moving back, we will not let our lives to be determined by fear,” he told a press conference in Berlin.

De Maiziere said a meeting of interior ministers of federal states agreed to keep the markets open and evaluate possible additional security on a case-by-case basis.

Around 2,500 Christmas markets across Germany are popular attractions and are visited by millions of people during the last months of the year.

* Anadolu Agency Washington Correspondent Michael Hernandez contributed to this report