PHNOM PENH, Cambodia (AP) — President Joe Biden and the leaders of Japan and South Korea on Sunday vowed a unified, coordinated response to North Korea’s threatening nuclear and ballistic missile programmes, with Biden declaring that the three-way partnership is “even more important than it’s ever been” when North Korea is stepping up its provocations.

Biden met separately with Japanese Prime Minister Fumio Kishida and South Korean President Yoon Suk Yeol before all three sat down together on the sidelines of the East Asia Summit in Cambodia.

The US president began by offering condolences for a crowd surge during Halloween festivities in Seoul that killed more than 150 people, saying the US had grieved with South Korea. The meeting was heavily focused on North Korean leader Kim Jong Un’s recent escalations, although Biden said the three leaders would also discuss strengthening supply chains and preserving peace across the Taiwan strait, while building on the countries’ support for Ukraine in the face of Russian aggression.

Biden had also planned to seek input from Kishida and Yoon on managing China’s assertive posture in the Pacific region on the eve of his face-to-face with President Xi Jinping.

“We face real challenges, but our countries are more aligned than ever, more prepared to take on those challenges than ever,” Biden said. “So I look forward to deepening the bonds of cooperation between our three countries.”

Both Yoon and Kishida discussed the ongoing displays of aggression by North Korea, which has fired dozens of missiles in recent weeks. The launches include an intercontinental ballistic missile 10 days ago that triggered evacuation alerts in northern Japan, and as the allies warn of a looming risk of the isolated country conducting its seventh nuclear test in the coming weeks.

Referring to the crowd surge that occurred in the Itaewon neighborhood in Seoul, Yoon said, through an interpreter: “At a time when South Koreans are grieving in deep sorrow, North Korea pushed ahead with such provocations which lays bare the Kim Jong Un regime’s true inclinations.”

US National Security Adviser Jake Sullivan told reporters on Saturday that Biden would use the meetings to strengthen the three countries’ joint response to the dangers posed by North Korea, officially known as the Democratic People’s Republic of Korea.

“What we would really like to see is enhanced trilateral security cooperation where the three countries are all coming together,” he said. “That’s acutely true with respect to the DPRK because of the common threat and challenge we all face, but it’s also true, more broadly, about our capacity to work together to enhance overall peace and stability in the region.”

Tensions on the Korean peninsula have skyrocketed in recent months as the North continues its weapons demonstrations and the US and South Korea launched stepped-up joint defense exercises. Earlier this month, the South Korean military said two B-1B bombers trained with four US F-16 fighter jets and four South Korean F-35 jets during the last day of “Vigilant Storm” joint air force drills. It was the first time since December 2017 that the bombers were deployed to the Korean Peninsula. The exercise involved a total of roughly 240 warplanes, including advanced F-35 fighter jets from both countries.