A government-wide inquiry into the preferential hiring of former public servants will be launched next week, the minister in charge of civil service reform said Friday.

The education ministry's systematic involvement in illegally helping a senior official land a plum post-retirement job also requires third-party involvement in the investigation, Kozo Yamamoto said.

"It is important to have a knowledgeable third party look into the matter so that no such issues will occur," Yamamoto told a news conference.

He said the probe into the latest case of amakudari (descent from heaven) will be led by the Cabinet Bureau of Personnel Affairs. But he declined to give further details on how it will be conducted, saying that doing so could hinder it.

In amakudari, retiring bureaucrats are hired by entities in the industries they once oversaw as public servants.

Prime Minister Shinzo Abe has instructed Yamamoto to carry out a probe covering all ministries and agencies to alleviate public concerns about the shady tradition.

The ministry's top bureaucrat resigned and other officials were reprimanded last week after a government watchdog found that it had helped a director-general secure a professorship in 2015 and tried to cover it up by preparing questions and answers for the parties involved in the event that they were questioned.