The chief government spokesman during Japan's nuclear crisis testified Sunday that he did not deliberately mislead the public about the extent of the accident.
Trade and industry minister Yukio Edano told a parliamentary investigative panel that the government did not fully understand the damage at the Fukushima Dai-ichi power plant after a massive earthquake and tsunami last year.
Edano has been accused of failing to provide full information about the accident and of downplaying health dangers.
He denied there was any cover-up and said he repeatedly used the phrases "no immediate risk" and "just to be safe" in his briefings because that's what officials believed at the time.
"I'm sorry for our misjudgment," he said.
Eventually, the government acknowledged that three reactor cores had melted at the plant in the worst nuclear accident since Chernobyl.
The parliamentary panel is the only public inquiry into the accident at which top nuclear regulators and officials from the plant's operator have testified. Former Prime Minister Naoto Kan, who led disaster management at the height of the crisis, is to testify on Monday.
A separate independent investigation said in a report in February that the government withheld information about the full danger of the disaster from its own people and from the U.S., causing public distrust and straining relations with Japan's biggest ally.
Edano said the U.S. government was obviously frustrated by the scattered information provided by Japan and sought to place American nuclear experts at the prime minister's office, but he refused, citing Japanese sovereignty. He said the request came through U.S. Ambassador John Roos three days after the disaster hit.
"I declined the request," Edano said. "The prime minister's office is a place to make decisions as a sovereign nation and it was not desirable to have foreign officials stationed there."