In its new defense buildup guidelines, Japan is considering including a pledge to improve the transparency and efficiency of its procurement process for U.S. military equipment amid concerns over its rising defense budget, government sources said Friday.

Japan purchases U.S. defense equipment mainly through a foreign military sales arrangement, which Washington uses to prevent sensitive military technology from leaking. But critics say it leads Tokyo to buy equipment at high prices.

The government had touched on the need to curb defense equipment costs "in general" in the past, but it is considering referring to "improving the foreign military sales system" for the first time in the guidelines as procurement costs under the arrangement are increasing, one of the sources said.