The leaders of Japan, China and South Korea agreed Wednesday to work together toward the complete denuclearization of North Korea as the world looks ahead to the first-ever U.S.-North Korea summit in the coming weeks.

"We have to build on the momentum toward the complete denuclearization of the Korean Peninsula, and peace and stability in Northeast Asia, and ensure North Korea takes concrete actions," Japanese Prime Minister Shinzo Abe said in a press conference after the trilateral summit.

The talks involving Abe, Chinese Premier Li Keqiang and South Korean President Moon Jae In were held in Tokyo's Akasaka Palace state guesthouse.

"We stress that it is only the international cooperation on and the comprehensive resolution of concerns of the parties...that will pave the way for the bright future for the DPRK," the leaders said in a joint declaration, using the acronym for North Korea's formal name, the Democratic People's Republic of Korea.

But it is unclear whether the three neighbors are completely on the same page due to their differing approaches toward the shared goal.

(From left, Abe, Moon and Li ahead of Wednesday's trilateral summit in Tokyo.)

It took more than half a day for the joint declaration to be issued due to differences over its wording and content, including a description of the history of the relationship between Japan and China, a negotiation source said.

On North Korea, Japan hoped to incorporate the phrase "complete, verifiable and irreversible denuclearization," according to the source. But the full phrase did not appear in the declaration apparently due to China's reluctance.

At the press conference, Li welcomed the recent pursuit of dialogue to resolve the North Korean nuclear issue. China, which is North Korea's main ally and trading partner, appears to be placing emphasis on dialogue and incremental rewards for Pyongyang, such as the easing of economic sanctions, in return for its phased elimination of nuclear weapons.

While keeping in sync with the United States and Japan in maintaining pressure on North Korea, South Korea has pursued a policy of inter-Korean dialogue under Moon.

Moon welcomed support by Japan and China for a declaration released after last month's inter-Korean summit confirming the goal of the "complete" denuclearization of the peninsula.

During the talks between Moon and the North's leader Kim Jong Un in the truce village of Panmunjeom on April 27, the leaders also agreed to strive to declare a formal end to the 1950-1953 Korean War.

On Wednesday, the three leaders released a separate statement that hailed the Panmunjeom Declaration.

The "annual" Japan-China-South Korea summit -- the seventh of its kind -- comes after the historic meeting between Moon and Kim, and ahead of the unprecedented U.S.-North Korean summit between President Donald Trump and Kim expected by early June.

In a meeting with Chinese President Xi Jinping in Beijing on March 26, Kim promised a nuclear-free peninsula.

The North Korean leader also met with Xi on Monday and Tuesday during a surprise visit to the port city of Dalian in northeastern China, according to China's official Xinhua News Agency.

Abe added at Wednesday's press conference that China and South Korea will support Japan's efforts to resolve the issue of Japanese nationals abducted by North Korea in the 1970s and 1980s.

Li and Moon "hope that the abductions issue between Japan and the DPRK will be resolved through dialogue as soon as possible," the declaration said.

On the economic front, the leaders underscored the importance of better connectivity in East Asia, saying they are committed to promoting infrastructure cooperation, according to the declaration.

The leaders of the three Asian powers, which together account for over 20 percent of the global economy, reaffirmed the necessity of free trade amid a lingering trade dispute between China and the United States. Trump has said he prefers bilateral trade deals over multilateral ones.

Abe, Li and Moon agreed to step up negotiations on a trilateral free trade agreement and a wider deal including Southeast Asia, India, Australia and New Zealand called the Regional Comprehensive Economic Partnership.

"There is currently great momentum toward globalization. We three can together become new drivers of global economic growth by cooperating in maintaining free trade and making investment easier," Li said after the summit in a speech to business leaders from the three countries.

Abe, Li and Moon also agreed to promote people-to-people exchanges as Japan is scheduled to host the 2020 Tokyo Summer Olympic Games and China the 2022 Beijing Winter Games, following the Pyeongchang Winter Games in South Korea in February this year.

(From left, Li, Abe and Moon)

Since 2008, the three countries have taken turns to host the gatherings, which have sometimes been put on hold due to Japan's chilled ties with its two neighbors over historical and territorial disputes, as well as political turmoil in South Korea.

Li expressed his country's readiness to host the trilateral summit on a regular basis, as China is expected to chair it next time.

Li arrived in Japan on Tuesday on his first visit since assuming the post of premier in 2013. Moon paid his first visit since becoming president in 2017.

Li is the first Chinese premier to travel to Japan in seven years and Moon's visit is the first by a South Korean president in nearly six and a half years.