Prosecutors have grilled Yoshimi Watanabe, the former head of Your Party, a tiny and now-defunct opposition group, for allegedly breaking the Political Funds Control Law, sources close to the investigation said.

Watanabe, a 62-year-old Diet veteran who lost his seat in last Sunday's general election, borrowed ¥90 million from a bank account linked to his political group in 2010. He also borrowed ¥80 million from the same account in 2013.

But neither of the transactions was recorded in the group's political funds report, in a potential violation of the law.

The Tokyo District Public Prosecutor's Office's special investigative squad has quizzed Watanabe on a voluntary basis to decide whether to pursue criminal charges against members of his group involved in drafting the report, the sources said Friday.

"We will sincerely explain that there is no problem from the viewpoint of the Political Funds Control Law," Watanabe's office said in a statement issued the same day.

When he quit as Your Party leader in April, Watanabe was embroiled in a massive scandal over his receipt of separate unreported loans totaling ¥800 million from the chairman of cosmetics firm DHC Corp.