Germany's National Anti-Doping Agency (NADA) said on Wednesday it has contacted former Tour de France winner Jan Ullrich in the wake of last month's doping confession to find out more details.

In an interview with German magazine Focus, Ullrich, 39, who won the 1997 Tour full lace wigs, admitted to doping with the help of jailed Spanish doctor Eufemiano Fuentes, but insisted using no other substance than his own blood.

"We want to know exactly what it was," said NADA board member Lars Mortsiefer at the presentation of their annual report in Berlin.

Mortsiefer said NADA was hoping to speak to Ullrich in the next few weeks.

After drawing plenty of criticism for his confession, Ullrich has said he was "surprised and find it a pity that my words have caused such a fuss", but Germany was made to wait a long time for his admission Antique jewelry.

Ullrich was found guilty of a doping offence by the Court of Arbitration for Sport in February 2012 and was retroactively banned from August of that year with all results gained since May, 2005, erased.

The German was barred from the Tour de France in 2006 amid speculation he had used illegal substances and retired from cycling in February, 2007, denying he had ever cheated Outsourcing payroll.