Japan will introduce four airborne refueling planes to help extend the flight range of Self-Defense Forces aircraft in its midterm defense buildup plan for the five years from fiscal 2001, coalition sources said Thursday.

In drafting the budget for fiscal 2001, which begins April 1, the government will seek appropriations for "research costs" to prepare for the introduction of the aerial tankers, they said.

Within the tripartite coalition, New Komeito had voiced concern over including aerial tankers in the next five-year midterm defense plan.