Opposition lawmakers grilled Defense Minister Shigeru Ishiba on Sunday over a widening defense funding scandal and said Japan should not resume aid to U.S.-led operations in Afghanistan before the allegations are cleared up.

Addressing the opposition legislators' questions on a TV talk show, Ishiba promised a comprehensive investigation.

Prosecutors raided the Defense Ministry last week over the scandal, which has triggered the arrest of former Vice Defense Minister Takemasa Moriya over allegations he was bribed by a contractor.

The opposition bloc has used the scandal to slow progress on legislation to renew the Self-Defense Force's mission to supply fuel to warships participating in U.S.-led operations in Afghanistan.

Speaking on the talk show, opposition legislators said the recent disclosures were indicative of bribery at top levels of the ministry, and that renewal of the refueling activities is out of the question until all allegations are cleared up.

"The problem doesn't lie just with Moriya. It goes much, much deeper than that," said Keiichiro Asao of the Democratic Party of Japan.

"We shouldn't be giving out oil, we should be draining the pus from a corrupt system," said Akira Kasai of the Japanese Communist Party.

Ishiba said the Defense Ministry will investigate and consider reforms.

"It is true the arrest of a top bureaucrat reveals structural faults with defense administration," Ishiba told the talk show. "We must thoroughly discuss reform measures in the Diet."