He told reporters that it was “gut wrenching” to leave many of his goals unfinished.

Abe has had ulcerative colitis since he was a teenager and has said the condition was controlled with treatment.

Concerns about his health began this summer and grew this month when he visited a Tokyo hospital two weeks in a row for unspecified health checkups. He is now on a new treatment that requires IV injections, he said.

While there is some improvement, there is no guarantee that it will cure his condition and so he decided to step down after treatment Monday, he said.

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“It is gut wrenching to have to leave my job before accomplishing my goals,” Abe said Friday, mentioning his failure to resolve the issue of Japanese abducted years ago by North Korea, a territorial dispute with Russia and a revision of Japan's war-renouncing constitution.

He said his health problem was under control until earlier this year but was found to have worsened in June when he had an annual checkup.

“Faced with the illness and treatment, as well as the pain of lacking physical strength ... I decided I should not stay on as prime minister when I'm no longer capable of living up to the people's expectations with confidence,” Abe said at a news conference.

In a country once known for its short-tenured prime ministers, the departure marks the end of an unusual era of stability that saw the Japanese leader strike up strong ties with U.S. President Donald Trump even as Abe's ultra-nationalism riled the Koreas and China.

While he pulled Japan out of recession, the economy has been battered anew by the coronavirus pandemic, and Abe has failed to achieve his cherished goal of formally rewriting the U.S.-drafted pacifist constitution because of poor public support.

Abe said he achieved a stronger Japan-U.S. security alliance and the first visit by a serving U.S. president to the atom-bombed city of Hiroshima. He also helped Tokyo gain the right to host the 2020 Olympics by pledging that a disaster at the Fukushima nuclear plant was “under control” when it was not.

Abe’s political career

Abe is a political blue blood who was groomed to follow in the footsteps of his grandfather, former Prime Minister Nobusuke Kishi. His political rhetoric often focused on making Japan a “normal” and “beautiful” nation with a stronger military and bigger role in international affairs.

Abe, whose term ends in September 2021, is expected to stay on until a new party leader is elected and formally approved by the parliament, a process which is expected to take several weeks.

Abe became Japan’s youngest prime minister in 2006, at age 52, but his overly nationalistic first stint abruptly ended a year later because of his health.

In December 2012, Abe returned to power, prioritizing economic measures over his nationalist agenda. He won six national elections and built a rock-solid grip on power, bolstering Japan’s defense role and capability and its security alliance with the U.S. He also stepped up patriotic education at schools and raised Japan’s international profile.

Abe on Monday became Japan’s longest-serving prime minister by consecutive days in office, eclipsing the record of Eisaku Sato, his great-uncle, who served 2,798 days from 1964 to 1972.

But his second hospital visit Monday accelerated speculation and political maneuvering toward a post-Abe regime.