TOKYO (AP) — Japanese transport ministry officials inspected Toyota subsidiary Daihatsu on Thursday, one day after officials announced it was suspending the small car unit's shipments of all vehicles in and outside Japan after an investigation found improper testing involving 64 models.

The safety test irregularities earlier this year prompted an independent panel investigation, which found widespread and systematic problems at Osaka-based Daihatsu Motor Co. It is the latest of safety or other violations found at at least five of Japan's major automakers in recent years.

On Thursday, transport ministry officials began a deeper investigation at Daihatsu's offices over the systematic safety scandal that apparently persisted for decades.

"It's extremely regrettable," Chief Cabinet Secretary Yoshimasa Hayashi said Thursday. "It damaged the trust of car owners and has shaken the foundation of the automobile certification system." Hayashi urged Daihatsu officials to fully explain the situation.

So far, there have been no reports of accidents or deaths due to the fudging of those tests.

Toyota Motor Corp., citing results of the panel, said Wednesday that the Daihatsu probe found 174 new cases of irregularities in safety tests and other procedures in 25 test categories, on top of problems reported earlier.

"We are sorry to have betrayed the trust of our customers," Daihatsu President Soichiro Okudaira told a news conference Wednesday. He acknowledged the cheating on safety testing and procedures was tantamount to neglect of safety certificates.

"We take it very seriously as the problem that has shaken the foundation of an automaker," he said.

A lawyer and a member of the probe team, Makoto Kaiami, who also attended the news conference, said workers under pressure to meet management demands for tight development deadlines resorted to cheating, and that the management should take the blame.

The issue first emerged in April when Daihatsu reported improper testing on door linings. Problems in the side collision testing also surfaced in May, officials said. The also found data falsifications and use of unauthorized testing procedures.

The problems were found in 64 models and three vehicle engines, including 22 models and an engine sold by Toyota, Daihatsu said in a statement. The investigation also found the problems affected some models of Mazda Motor Corp. and Subaru Corp. sold in Japan, and Toyota and Daihatsu models sold abroad.

Daihatsu is Toyota's unit specializing in small cars and trucks that are popular in Japan.

Toyota expressed "sincere apologies."

"We believe in order to prevent a recurrence, in addition to a review of certification operations, a fundamental reform is needed to revitalize Daihatsu as a company," Toyota said in a statement.

Toyota said it will review Daihatsu's management and business operations, organization and structure, as well as the mindset of employees. It will provide full support to revitalize Daihatsu, it said.