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Masatsugu Asakawa, Japan's top financial diplomat, would attend the G20 meeting in Aso's place if he chose not to go, the sources with knowledge of the plans told Reuters.
Premier Shinzo Abe and Aso, his close ally, are under pressure following the finance ministry's announcement it had altered records of a discounted sale of state-owned land to a school operator with ties to Abe's wife.