By Yoko Wakatsuki and Joshua Berlinger, CNN

(CNN) -- Japanese Prime Minister Shinzo Abe has promised to take a firm stance on North Korea, after a predicted landslide win in Sunday's parliamentary elections.

"My immediate task is to deal with North Korea," Abe told reporters. "It will take tough diplomacy. With the mandate given by the people, I would like to exercise my command in diplomacy."

Abe had called the snap vote to seek a boost to his parliamentary majority and is likely to use any new powers to attempt to overhaul the country's defense strategy and pacifist stance.

An exit poll by public broadcaster NHK forecast a decisive win for Abe's coalition, saying his conservative Liberal Democratic Party (LDP) would take 253 to 300 of Parliament's 465 seats. The Komeito party, which is in a coalition with the LDP, is predicted to take 27 to 36 seats.

Other local broadcasters reported well over 300 seats by the coalition. Exit polls are not final results and the official count is expected early Monday.

In the face of an increasingly hostile North Korea, Abe earlier this year set a deadline of 2020 to revise Japan's constitution, which contains language that bans Japan from maintaining armed forces. It is a controversial proposal that strikes at the heart of the country's post-war identity.

The forecast win also puts Abe, 63, on track to become the longest-serving leader in the country's modern history. His performance at the polls Sunday is an indication his party is likely to re-elect him as their leader for another three years.

"I must face with this victory with humility," Abe told NHK after the exit poll results. "The voters gave us, the ruling party, a majority. This is the voice of the Japanese people, telling us to push our policies forward and come out with results."

Opposition in disarray

Abe had sought to win a two-thirds "super majority" in Parliament, which would help him achieve his goal of amending the constitution.

He would need 310 seats to achieve that balance of power, and while some exit polls show Abe passing that threshold, others do not.

Abe called the election at a key moment when the opposition was in disarray, and his popularity ratings began to pick up after months in the doldrums.

He ran with very little opposition. Tokyo Governor Yuriko Koike launched her conservative Party of Hope ahead of the poll, splintering the traditional opposition.

But Koike did not herself run for a seat in Parliament and her party failed to put forward a viable candidate. Koike was in Paris during the vote Sunday on a scheduled official trip.

"It is a very tough result. We will analyze the reason for the defeat," she told NHK.

North Korea threat

Japan has faced increased hostility from North Korea in recent months, as the rogue state locks horns with the Trump administration over Pyongyang's missile and nuclear programs.

Pyongyang flew two projectiles over Japan last month, including a ballistic missile, in act of defiance against Washington and the international community.

But Japan's ability to respond is limited. Its constitution does not allow Japan's military -- called the Self-Defense Forces -- to develop significant offensive capabilities. Article 9 of the constitution says that "land, sea and air forces, as well as other war potential will never be maintained."

Neighbors that suffered under Japanese occupation during World War II view Abe's ambitions with concern and skepticism. It's also highly controversial in Japan itself, to the point where lawmakers came to blows debating the issue in 2015.

But altering Japan's constitution is a heavy lift. Even with strong parliamentary support, such a measure must be approved in a referendum.

The Trump factor

One of the first items on Abe's agenda will be US President Donald Trump's first trip to Asia while in office early next month.

Trump's talk of turning inward has had US allies in the region worried that they can no longer rely on the US for defense as they once did. Some Japanese hawks have pointed to this as yet another impetus to revise the constitution.

Abe has invested significant time and effort into his relationship with his new US counterpart, becoming the first foreign leader to meet with Trump when he was President-elect and during a summit in February at Trump's Mar-a-Lago estate, where the two played golf together.

Today, the two are bound by their shared hard line on Pyongyang -- both have been vociferous in their opposition to North Korea's missile and nuclear tests.

The-CNN-Wire

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