The commander of the U.S. Navy's Pacific Fleet said Tuesday that China's military budget has a troubling lack of transparency, a day after Beijing announced the biggest hike in military spending in three years.

China on Monday unveiled an 8.1 percent rise in defense spending for 2018, fueling an ambitious military modernization program and making its neighbors, particularly Japan and self-ruled Taiwan, nervous.

"These investments and commitment need to be taken with full transparency," Adm. Scott Swift said during a press roundtable in Tokyo. China's "intent is not clearly understood."