Satsuki Katayama, a veteran politician of the ruling Liberal Democratic Party, publicly apologized to the Democratic Party of Japan on Wednesday for her tweet claiming the largest opposition force had, when it was the ruling party, downgraded the government's monitoring of Mount Ontake.

Katayama, an Upper House member, deleted her Sunday tweet that suggested monitoring of the mountain was inadequate because of the DPJ's downgrading, making it difficult to predict an eruption, and posted a new tweet apologizing to the DPJ. The volcano erupted Saturday, claiming dozens of lives.

The DPJ had protested the tweet Wednesday, calling the remark unfounded.

"It was a comment based on erroneous understanding of facts," said Katayama in the new tweet. "I am deleting it and sincerely apologize (to the DPJ)."

The LDP also conveyed her apology to the DPJ, and Katayama is scheduled to explain the circumstances that led to her tweet and express her apology at a meeting of the Upper House Foreign Affairs and Defense Committee, which she chairs, on Thursday.

In the tweet in question, Katayama said Mount Ontake had been excluded from regular monitoring for signs of an eruption as part of a major budget screening initiated by the DPJ in its capacity as the ruling party before the LDP returned to power in 2012, quoting a local government leader, without mentioning who it was.

The DPJ on Wednesday lodged a protest with the LDP and Katayama for the remark in a letter, after confirming her remark was not true. Upon receiving the protest, the LDP executives spoke to Katayama and sternly reprimanded her, according to sources.