(CNN Business) Japanese officials on Sunday criticized Carlos Ghosn's escape from the country as "unjust" and vowed to tighten immigration rules in their first public remarks since the former auto executive fled for Lebanon a week ago.

Ghosn left Japan "illegally by unjust methods," said Justice Minister Masako Mori, the country's top judicial official. She said that authorities have no official record of Ghosn's departure from Japan, and that prosecutors are investigating the case.

Mori also said she has ordered the country's immigration department to "further tighten" rules for leaving the country "so that the same situation won't be repeated."

Mori's statement — along with a similar one published Sunday by a Tokyo prosecutor — marked the first time Japanese authorities addressed Ghosn's stunning escape last week. Government offices in the country had been closed all week for the New Year holiday.

Ghosn — the former chairman of Nissan and Mitsubishi Motors, and former chairman and CEO of their alliance partner, Renault — had been awaiting trial in Japan on charges of financial wrongdoing . As a condition of his release on bail, Ghosn was required to stay in Japan. But the case was upended after Ghosn revealed that he had fled Japan for Lebanon to escape what he called a "rigged" justice system.

Read More