German Chancellor Angela Merkel is pledging to deploy the full force of the law in investigating Monday's deadly attack on a Berlin Christmas market as Germany mourns the "horrific and unimaginable" deaths and injuries.

Merkel said she had spoken with President Obama after the attack and that Obama pledged the United States' support in investigating the incident, which authorities believe was an intentional attack.

Merkel said she is "shocked, shaken and deeply saddened" by the attack, adding that it would be "particularly sickening" if the attacker was seeking refuge in Germany.

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The White House on Tuesday confirmed Obama’s call with Merkel and reiterated his pledge of support. 

“The president offered his condolences, and those of the American people, for the horrific apparent terrorist attack against the Berlin,” The White House said in a statement. “No attack could sway our determination — and that of our German allies — to defeat terrorism in all of its forms.”

A suspect arrested after the attack "comes from Pakistan" and had applied for asylum, Interior Minister Thomas de Maiziere said Tuesday. 

De Maiziere said the suspect, who has denied any involvement, came to Germany late last year and to Berlin in February.

The suspect did not have a record of terrorism, according to The Guardian.

At least 12 people were killed and many more injured when a truck plowed into a busy market. One of the 12 people who died was found in the passenger seat of the truck and had been shot with a pistol.

De Maiziere told reporters we "must not compromise our lifestyle."

"If we do that, the enemies of freedom have already won," he said.

"We are deeply saddened but we also fight for freedom."

Jordan Fabian contributed.

This report was updated at 7:32 a.m.