Donald Trump says attacks like Berlin rampage are purely religious threat

US president-elect Donald Trump claimed on Friday that attacks like the one in Berlin is a "purely religious threat which turned into reality" as he referred to the suspected attacker's video in which he talked about slaughtering crusaders who had come to kill Muslims.

"The terrorist who killed so many people in Germany said just before crime, "by God's will we will slaughter you..." This is a purely religious threat, which turned into reality," Trump tweeted in two tweets.

"Such hatred! When will the US, and all countries, fight back?" Trump asked.

The alleged Berlin attacker Anis Amri, 24, from Tunisia posted a video prior to the attack on social media. During the two-minute, 42-second video, Amri, who was killed by police in Milan, is shown speaking directly to a camera and pledging allegiance to the Islamic State (IS).

Amri also declared his desire to avenge Muslims killed in airstrikes and called for attacks against "Crusaders".

Earlier this week, Trump told reporters that they "know my plans" when he was asked about his campaign statements about banning Muslims from entering the country.