A Tunisian asylum-seeker was arrested in Frankfurt on Wednesday on suspicion of planning a terrorist attack in Germany.

The 36-year-old man, named in the German press as Haikel S, is wanted in his native Tunisia in connection with a 2015 terror attack in which 21 people were killed, including one Briton.

He is believed to have been actively recruiting volunteers to carry out an attack in Germany on behalf of Islamic State of Iraq and the Levant (Isil), according to prosecutors.

But German authorities are facing tough questions over how the wanted man was able to slip into the country undetected posing as an asylum-seeker.

He had previously lived in Germany and has been known to police as a radical Islamist for ten years, according to claims in Welt newspaper.

Haikel S was held in a series of early morning raids on mosques, apartments and offices in Frankfurt and the surrounding state of Hesse.

Authorities in the state said the operation had broken up an “extensive” jihadist network.