Opposition parties Wednesday ramped up calls to extend the current Diet session, saying the government lied about the existence of backup data for a guest list to a state-funded cherry blossom-viewing party this year.

The recent furor over the event shows no signs of easing, despite Prime Minister Shinzo Abe's denials that he used it for personal gain. He also denies he invited a former chairman of a company suspected of fraudulent business activity.

"This is not going to end. We'd rather ask for an extension to the Diet session beyond the year's end," Jun Azumi, the Diet affairs chief of the main opposition Constitutional Democratic Party of Japan, told reporters. The current extraordinary session runs through next Monday.