TOKYO—Japanese Prime Minister Shinzo Abe said he hasn't decided whether to go ahead with a second sales-tax increase planned for next year, after senior members of his administration suggested the October 2015 increase shouldn't be delayed.

Mr. Abe told national broadcaster NHK that the increase was necessary to cover social-security payments, but the timetable depended on the health of the economy.

"As the economy is a living thing I want to be neutral in my thinking," Mr. Abe said, adding that he would pay close attention to growth figures for the July-September quarter following a 7.1% contraction in the economy in the previous quarter.

Mr. Abe is expected to make his decision on the second tax increase in early December, after revised growth figures for the third quarter are released.

The sudden dip in Japan's gross domestic product followed the first sales-tax increment in April. The increase in the tax to 8% from 5% hit consumption and whiplashed the economy after front-loaded demand powered growth to 6% in the January-March period. Economists generally expect the economy to pick up during the coming months, but questions remain whether the momentum will be strong enough to ride out a second tax increase, with some of Mr. Abe's policy advisers calling for him to hold off on the plan for now.