TOKYO — Voters on the southern Japanese islands of Okinawa re-elected a governor on Sunday who campaigned for the removal of an American Marine base there, throwing a wrench into a deal between Japan and the United States to relocate the base and posing a challenge for the United States as it grapples with a response to North Korean aggression.

Gov. Hirokazu Nakaima, 71, had once supported the plan to transfer the base to a less populated part of Okinawa, but he reversed himself after strong opposition by residents.

While his position was less strident than that of his main opponent, who called for the base to be removed from Japan altogether, Mr. Nakaima’s re-election still presents an obstacle to the Japanese-American agreement: any relocation of the base in Okinawa will require Mr. Nakaima’s approval....