The neo-Nazi network communicated with its members in German jails nationwide through letters and coded messages in the classified ads of magazines, according to a Wednesday report in the mass-circulation daily Bild.

Authorities in the state of Hessen uncovered the group after examining evidence collected during a search of prison cells last week. The network reportedly relies on a strongly hierarchal organizational structure.

Hessen's justice minister, Jörg-Uwe Hahn, told Bild that authorities were conducting a full investigation into how the network had gone undetected.

"We don't want to repeat the mistakes in the prison system that security authorities made in connection with the crimes of the NSU," Hahn said.

Security tightened in prisons

The daily Süddeutsche Zeitung newspaper has reported that prisons in Hessen have tightened security to crack down on the network.

Hahn's office confirmed reports that members of the neo-Nazi prison network had tried to contact members of the NSU. A cell of three NSU members allegedly murdered eight Turkish and one Greek shopkeeper as well as a German policewoman between 2000-2007.

Two alleged members of the cell, Uwe Mundlos and Uwe Böhnhardt, supposedly set their mobile home on fire and committed suicide in Eisenach after robbing a bank there in 2011.

Hours later, their apartment in the city of Zwickau was set on fire, allegedly by the third member, Beate Zschäpe, who goes on trial in Munich next week.

slk/kms(AP, AFP, dpa)