The unnamed 16-year-old boy was detained by a special counterterrorism unit late Tuesday in the refugee shelter where he lived in the Porz district of Cologne.

The teenager had been planning a bomb attack, police spokesman Klaus-Stephan Becker told journalists on Wednesday. In online chats, the boy expressed an "unequivocal willingness" to follow through on such a plot.

The young suspect received "very concrete instructions" from a chat partner abroad on how to build a bomb, added police chief Jürgen Mathies.

He said there was no evidence to suggest that the teen possessed the required materials for an explosive device.

Quickly radicalized

Police and prosecutors said information gleaned from his mobile phone showed he was in touch with IS and "wanted to recruit the young Syrian for Islamist activities," authorities said.

The statement did not say how it had intercepted the communications but did note that a 35-strong investigation team has been detailed to follow the case. Authorities added that it was believed his "radicalization" had begun relatively recently.

Prior to being detained, the teen was questioned three times by police over the past few months after authorities received tips from social workers and fellow refugees as well as a mosque in Cologne which suggested the teen had been rapidly radicalized.

Police noted that the teen came from a "good home" and that he was first registered in Germany along with his parents and sister in January 2015. His parents were academics who lived in Damascus before fleeing the Syrian civil war.

Germany is in a heightened state of alert following deadly attacks in neighboring France and Belgium as well as lone wolf attacks in which young asylum seekers were apparently "radicalized" and went on rampages such as the axe-attack on a train in Würzburg and a suicide bombing in Ansbach.

Both attacks rattled Germans' sense of security and fuelled concerns over the country's record influx of migrants and refugees last year.

rs, jar/jil (AP, AFP, dpa, Reuters)