When foreign ministers from China, Japan and South Korea meet in Tokyo on Wednesday to discuss trilateral cooperation, the missile and nuclear tests by the Democratic People's Republic of Korea (DPRK) and the planned deployment of a missile defense system in South Korea should be at the top of the agenda, according to experts.

In announcing the meeting on Monday, China's Foreign Ministry spokesman Lu Kang said that the three countries have held a range of key meetings and events promoting trilateral cooperation in all fields.

Cooperation initiated 17 years ago has "played a constructive role" in boosting regional peace and stability, Lu said.

The Japanese Foreign Ministry said that Foreign Minister Fumio Kishida will host a dinner for his Chinese and South Korean counterparts, Wang Yi and Yun Byung-se, on Tuesday, with an official trilateral meeting set for Wednesday.

Ted Carpenter, a senior fellow at the Cato Institute, said the DPRK issue will likely dominate the talks, although China will certainly bring up the THAAD (Terminal High Altitude Area Defense) deployment issue.

"The US will especially be looking for progress on the North Korea issue," he said, adding that territorial disputes could be a source of disruption in the talks. Japan has maritime territorial disputes with both China and South Korea.

DPRK has conducted several nuclear and missile tests and firings this year, raising concerns in the region and the world.

Meanwhile, the decision in early July by South Korea and the US to deploy the THAAD missile defense system in South Korea has angered China and Russia. Both see it as a threat to their national security and a scheme masterminded by the US.

Zhiqun Zhu, professor of political science and international relations at Bucknell University, believes the most important issues for the trilateral talks will be security and the economy.

"For all three countries, North Korea's nuclear program is a common challenge," he said. "They should narrow their differences and find some common ground on how to best approach the North Korea challenge."

Zhu also said that the three countries need to ensure that political differences will not hinder economic cooperation. "They need to push forward the idea of a trilateral free trade agreement," he said.

The Korea Times earlier quoted South Korea Deputy Trade Minister Kim Hak-do as saying that the three countries must cooperate to overcome the negative impact from the Brexit.

The three countries have held 10 rounds of FTA talks since negotiations started in 2012. During the trilateral summit between Chinese Premier Li Keqiang, South Korean President Park and Japanese Prime Minister Abe last November, they agreed to speed up the talks and aim for a "comprehensive, high-level and mutually beneficial" agreement.

"It is a very difficult time when China-Japan and China-ROK relations are both tense," Zhu said. "The ministerial talks are important to help ease tensions and pave the way for summit meetings during the G20."

There has been no announcement so far of any bilateral meetings at the upcoming G20 summit in Hangzhou between Chinese President Xi Jinping and South Korea President Park Geun-hye or Xi and Japanese Prime Minister Shinzo Abe.

Zhu noted that while a trilateral summit by the end of the year is probably not realistic, bilateral summits — especially on the sidelines of an international conference — should be promoted as a way to move the relationship forward.

Guo Yanjun, deputy director of the Institute of Asian Studies at China Foreign Affairs University, said the timing of the annual ministers' meeting was "ideal" in light of the recent difficulties.

"Their plan to sit at the same table again shows there's a political will to improve ties," Guo said.

The three sides "have tried their best to keep bilateral issues away from the trilateral agenda," Guo added. "They are taking a positive attitude. And further trilateral cooperation, in return, will be helpful for resolving two-way issues."

"The trilateral foreign ministers' meeting itself is already a victory," Guo said.

Tensions on the Korean Peninsula flared up this week when the US and South Korea on Monday began a 12-day annual military exercise known as Ulchi Freedom Guardian, involving 25,000 US troops and 50,000 South Koreans.

On Monday, Pentagon spokesman Peter Cook described the drills, in existence since 1976, as defensive in nature. "Of course, the reason we are doing those kinds of things is because we see the kind of provocative action the North Koreans have taken recently," he told the daily press briefing.

DPRK has responded strongly to the drills. The DPRK will "turn the stronghold of provocation into a heap of ashes through Korean-style pre-emptive nuclear strike" if the US and South Korea "show the slightest sign of aggression" during the drills, a spokesman for North Korea's military was quoted as saying by the country's state media, according to a CNN report.