After drawing fire from the opposition camp, a key adviser to Prime Minister Shinzo Abe on Monday retracted his remarks downplaying the need for the national security bills currently being debated in the Upper House to be consistent with the Constitution.

Summoned before an Upper House special committee as an unsworn witness, Yosuke Isozaki apologized for his remarks last week in which he said: "What we need to consider is whether the measures are necessary to protect Japan. Legal stability does not matter."

Isozaki, however, brushed off calls to step down as an adviser to Abe, saying he will fulfill his responsibilities by concentrating on his job as an aide to the prime minister.