The head of Tokyo Electric Power Co. apologized Tuesday over his predecessor’s order to not use the term “core meltdown” to describe the situation at the Fukushima No. 1 nuclear plant in the early days of the March 2011 crisis.

“It is extremely regrettable. People are justified in thinking it as a coverup,” Tepco President Naomi Hirose said at a news conference in Tokyo.

The remarks came after a report published last Thursday said that then-President Masataka Shimizu instructed a vice president, who was taking part in a news conference on March 14, 2011, not to use “core meltdown” to describe the states of the reactors.

Tepco reported to authorities on March 14, based on a computer simulation, that the event damaged 25 to 55 percent of the fuel rods, but the utility did not say it constituted a meltdown, the report said.

The company’s internal manual defined a meltdown as damage to more than 5 percent of the fuel.

The utility used the less serious phrase “core damage” for two months after the disaster began. In May 2011, Tepco finally used “meltdown.”

The report suggested that efforts were made to make the nuclear crisis look less severe than it actually was at a time when attention was riveted on the condition of the six-reactor complex following a massive earthquake and tsunami that devastated northeastern Japan on March 11, 2011.

The utility said it will cut Hirose’s salary by 10 percent for a month.

Shimizu likely issued the instruction due to pressure from the office of then-Prime Minister Naoto Kan, according to the report, compiled by a third-party commission set up to investigate the utility’s handling of the disaster. But it did not explain how pressure was exerted by the prime minister’s office, citing fading memories of the people involved.

The commission said it had not interviewed Kan or Yukio Edano, who was then chief Cabinet secretary in the administration, in the course of compiling the report because it was not authorized to do so.

The two denied the allegation.

On Friday, Edano called a special news conference to refute the panel’s finding, saying that neither he nor Kan ordered or requested then-President Shimizu to avoid using the term “meltdown” under any circumstance.

He said the party will consider taking legal action against Tepco and a third-party panel that compiled the report. Edano criticized the report as “inadequate and unilateral.”

Edano also said the timing of the report was suspicious ahead of the Upper House election. Kan has suggested it might be some kind of bid by Tepco and the ruling parties to sling mud on the opposition Democratic Party.

The DP is the successor to the Democratic Party of Japan, to which Kan and Edano belonged, before it merged with Ishin no To (Japan Innovation Party) on March 27.