Prosecutors are poised to question former Daio Paper Corp. Chairman Mototaka Ikawa and launch a full investigation as early as next week over more than ¥10 billion in dubious loans he took out from Daio group firms, sources said.

Tokyo prosecutors have already grilled executives of the subsidiaries and others involved, and are believed nearing the final stages of their probe, the sources said Thursday, adding Daio, which has been moved to the Tokyo Stock Exchange's watch list for possible delisting, is expected to file a criminal complaint against Ikawa on suspicion of aggravated breach of trust.

Loans totaling ¥10.68 billion were borrowed in 26 installments from seven subsidiaries between May 12, 2010, and Sept. 6, 2011. Ikawa, a grandson of company founder Isekichi Ikawa, has repaid ¥4.75 billion but is believed to have lost much of the money gambling at casinos in Macau.