Prime Minister Shinzo Abe, Japan's longest-serving premier, announced his resignation because of poor health on Friday, ending a stint at the helm of the world's third-biggest economy in which he sought to revive growth and bolster its defences.

"I have decided that I will step down as prime minister, with the belief that I cannot continue being prime minister if I do not have the confidence that I can carry out the job entrusted to me by the people," Abe, 65, told a news conference...