German police
German policeReuters

A 16-year-old Syrian refugee has been arrested in Germany on suspicion of planning a bomb attack in the name of the Islamic State jihadist group (ISIS), officials said Wednesday.

The youngster, thought to have been radicalized only recently, was detained in a special forces operation late Tuesday at a shelter for asylum-seekers in the western city of Cologne, police and prosecutors said.

Initial information gathered from the teenager's mobile phone showed that he had expressed an "unmistakable willingness" to carry out an attack, Klaus-Stephan Becker of the Cologne police told reporters.

Investigators had found a series of online chat messages that contained "concrete instructions for building explosive devices" as well as tips on how to cause maximum damage, added local prosecutor Ulf Willuhn at the same news conference.

It was not immediately clear how far the plans for an attack had progressed, he said.

According to an earlier statement by police and prosecutors, conversations found on the teenager's phone had indicated he was in touch with a person abroad who had ties to ISIS and "wanted to recruit the young Syrian for Islamist activities".

German security authorities described the suspect as a "serious threat" and have assigned a 35-strong team of investigators to the case.

Arutz Sheva Staff contributed to this report

The youngster is understood to have arrived in Germany with his family last year.

He had already been brought to the attention of police twice before, after fellow residents and employees at his asylum-seekers' shelter voiced concerns that he had been radicalized. But police said there was not enough information to take action.

It was only after a mosque expressed similar suspicions that police were able to arrest him, Becker said.

The case comes a week after German police detained three men with forged Syrian passports accused of being ISIS militants and labelled a possible "sleeper cell" with links to the assailants behind the November attacks in Paris.

Germany is on edge after suffering two attacks claimed by ISIS in July - an axe rampage on a train in Wuerzburg that injured five and a suicide bombing in Ansbach that left 15 wounded. Both were carried out by asylum seekers.

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

German police say they have identified 523 people who pose a security threat to the country, around half of whom are known to be currently in Germany.