The main opposition party's leader demanded Monday that former President Lee Myung-bak testify before parliament over alleged irregularities in his past administration's overseas resources development projects.

The prosecution and the National Assembly have conducted separate investigations into allegations the former administration wasted billions of dollars by investing in overseas resources development projects that had few results. Lee, who was in office from 2008-2013, is affiliated with the ruling Saenuri Party.

According to the results of an inspection by the state audit agency announced Friday, three state-run energy companies -- Korea National Oil Corp., Korea Gas Corp. and Korea Resources Corp. -- have invested a total of 31.4 trillion won ($28.7 billion) since 2003 in energy projects abroad. Those projects, however, have resulted in a confirmed net loss of 3.4 trillion won so far, with further losses expected down the road.

Moon Jae-in, chairman of the New Politics Alliance for Democracy, proposed that both he and Lee testify before the National Assembly. Moon was chief of staff to Lee's predecessor, Roh Moo-hyun, who also carried out similar projects overseas.

"The Saenuri Party says former President Lee Myung-bak will appear as a witness if I appear as a witness," Moon said during a party meeting. "Fine. I will step forward. Former President Lee, please come forward."

Moon's demand comes one day before the parliamentary investigation is due to end. It has so far failed to prove the allegations.

Saenuri floor leader Yoo Seong-min, speaking to Yonhap News Agency by phone, said the party cannot ask Lee to appear before parliament without any evidence of wrongdoing.

Yoo added, however, that the party will consider extending the deadline of the parliamentary investigation. (Yonhap)