Japanese Prime Minister Shinzo Abe risks further alienating Asian neighbors China and South Korea if he does not stick to the substance of a 1995 apology for wartime aggression, former prime minister Tomiichi Murayama said on Tuesday.

Murayama, a socialist, was head of a coalition with the conservative Liberal Democratic Party two decades ago when he made the "heartfelt apology" for the wartime damage and suffering caused by Japan. Abe, then a rookie LDP lawmaker, was one of those who opposed the move.

Now premier for a second time, Abe's conservative agenda includes adopting a less apologetic tone toward the past and revising the postwar, pacifist Constitution.