Prime minister Boiko Borisov proposed that Germany's Siemens acquire the freight unit of state-owned railway holding company BDZ in exchange for BDZ's debt for the purchase of 50 trains seven years ago.
Borisov has already requested that Bulgarian officials approach Siemens with the offer, state-run Bulgarian News Agency (BTA) reported.
"We are inviting them to the bidding," BTA cited Borisov as saying at a joint news conference with the president of the Association of German Chambers of Industry and Commerce, Hans Heinrich Driftmann.
Bulgaria owes Germany some 300 million levs ($189 million/153 million euro) for the purchase of 50 Siemens multiple-unit trains in 2005, which was financed with a loan from KfW development bank. In 2010, BDZ stopped servicing the loan, which is partially guaranteed by the German government.
Earlier this year the Bulgarian government launched an attempt to privatise BDZ's freight unit. In July it cancelled the tender after it attracted only one bidder.