Without citing its sources, German weekly Der Spiegel said the two men exchanged messages with individuals using different phone numbers, including some that were registered in Saudi Arabia.

The Afghan teenager who in July went on an axe rampage on a train, wounding four tourists from Hong Kong and a German passer-by, had reportedly discussed how he would carry out the attack with his Isis contacts.

In one of the exchanges, an Isis contact suggested that the teen, named by German media as Riaz Khan Ahmadzai, could drive a car into a crowd, but the Afghan rejected the idea as he did not have a driver's licence, the report said.

The teen said he would instead get on a train and carry out his attack onboard.

Read more: The Local