'We have to assume this was a terrorist attack'- Merkel

German Chancellor Angela Merkel said on Tuesday that authorities believe a deadly rampage by a lorry driver at a Berlin Christmas market was a "terrorist" attack likely committed by an asylum seeker.

Merkel says she is "shocked, shaken and deeply saddened" by the attack that killed at least 12 people on Monday.

She told reporters on Tuesday that it would be "particularly sickening" if it turns out the attacker was an asylum-seeker who sought refuge in Germany.

German media have reported that a suspect arrested after the attack was a Pakistani citizen who came to Germany in late 2015 or early 2016.