The State Prosecutor's Office in Hannover said that 44-year-old Sebastian Edathy's offices in Nienburg and Stadthagen, near Hannover as well as his houses in Rehburg, in the state of Lower Saxony and in Berlin were searched by police on Monday.
The raids were "within the framework of an investigation" the prosecutor's office launched on Monday, a spokesperson said in a TV interview.
She declined to give any further details in view of the on-going investigations.
TV networks NDR and ZDF reported that Germany's Federal Criminal Office (BKA) had traced Edathy's name and his Internet protocol (IP) address when it carried out probe last year into the operations of an international child pornography syndicate and this may have triggered the investigations against him.
Edathy, who earlier served for three years as the interior affairs spokesman of his Social Democratic Party (SPD), was widely expected to grab a top job in the new Conservative-Social Democrat coalition government formed by chancellor Angela Merkel at the end of last year, three months after the parliamentary election in September.
But, he unexpectedly announced on Friday that he is laying down his parliamentary seat in the Bundestag after 15 years on health grounds.
Born in Hannover as the son of a migrant from Kerala and a German mother, dathy had a rapid rise in the SPD since joining the party in 1990.
The SPD leadership said yesterday that Edathy has been on medical leave since the beginning of January.
In his reaction to the opening of investigations against him, Edathy rejected the allegations as "pure speculation".
"Public allegations that I am in possession of child pornographic works or tried to obtain them are wrong," he said in a press statement on his Facebook site.
He said he did nothing which makes him liable to criminal prosecution.
Media commentators speculated Edathy may have laid down his parliamentary seat to facilitate investigations and to spare the Bundestag the need to lift his parliamentary immunity against prosecution.
Thomas Oppermann, chairman of the SPD parliamentary group in the Bundestag, said the allegations against Edathy are "extremely serious" and he urged the authorities to provide speedy and detailed clarifications.
Edathy had also served as the chairman of the Germany-India parliamentary group during 2003-2007.