File photo of Abe. (Photo: VCG)

TOKYO, Feb. 1 (Xinhua) -- Officials of the Japanese labor ministry had been aware of the faulty method in conducting wage surveys for more than a decade, the ministry said Friday.

The Ministry of Health, Labor and Welfare said regional bureau officials sent questionnaires by mail in the wage structure survey, whereas they should visit companies in person.

The misconduct dated back to 2006 and was not reported properly to the Ministry of Internal Affairs and Communications in charge of overseeing all governmental statistics.

Earlier in the day, a senior official in charge of the survey was dismissed for not reporting the discovery of the malpractice.

The latest development in the scandal involving the ministry has led to suspicion that there was an internal coverup, and delt a new blow to Japanese Prime Minister Shinzo Abe's administration.

Abe on Thursday vowed to conduct an independent probe into the flawed gathering of labor statistics that has dogged the labor ministry of late.

The government admitted on Jan. 11 that it had failed to pay more than 53.7 billion yen (495.7 million US dollars) in unemployment insurance, workers' compensation and sailors' insurance due to faulty jobs data.

The issue was revealed after the labor ministry was found to have published its monthly labor survey without collecting enough data.