SEOUL, South Korea (AP) — Senior officials from the United States, South Korea and Japan reaffirmed their countries' commitment Wednesday to finding a diplomatic solution to the threat posed by North Korea's rapidly expanding nuclear program. However, U.S. Deputy Secretary of State John Sullivan stressed that the allies must be prepared for any contingency.

After meeting with his South Korean and Japanese counterparts in Seoul, Sullivan said the U.S. continues to view diplomacy, supported by pressure and sanctions, as the primary means for solving the North Korean nuclear problem. But despite that approach, the Trump administration will continue to keep "all options on the table" because the "regime in Pyongyang is unpredictable and non-transparent," he said.

"Our objective is, throughout that campaign of pressure, to bring North Korea to the negotiating table without preconditions so that we can achieve our objective of a denuclearized Korean Peninsula," Sullivan said at a news conference after the meeting, where the officials mainly discussed responses to North Korea's nuclear activities.

"Diplomacy is our primary objective and primary means to addressing the threat posed by North Korea. But we need to be prepared to respond to any eventuality given the unpredictable nature of the regime in Pyongyang," he said.

Before flying to Seoul for talks with South Korean Vice Foreign Minister Lim Sung-nam, Sullivan and Japanese Deputy Foreign Minister Shinsuke Sugiyama met in Tokyo on Tuesday and vowed to find more ways to apply pressure on North Korea.

On Wednesday, Lim said the allies agree that the situation surrounding the Korean Peninsula should be "managed stably."

The vice-ministerial discussions were followed by a meeting of the countries' top envoys for currently stalled nuclear disarmament talks with North Korea that also involved China and Russia. The six-party talks were last held in late 2008 and North Korea went on to conduct its second nuclear test in May 2009.

South Korea's Foreign Ministry said the nuclear envoys agreed their countries must pursue every available avenue, including dialogue and sanctions, to peacefully achieve North Korea's complete denuclearization.

The Seoul meetings came as the U.S. and South Korea conduct joint naval drills involving fighter jets, submarines and other naval vessels, including the aircraft carrier USS Ronald Reagan, to train for potential North Korean provocations. The allies regularly conduct joint exercises that North Korea condemns as invasion rehearsals.

North Korea in recent months has tested purported thermonuclear weapons and intercontinental missiles and launched two midrange missiles over Japan while also threatening to fire similar weapons toward Guam, a Pacific U.S. territory and military hub.

North Korea's deputy U.N. ambassador, Kim In Ryong, said Tuesday at the United Nations that his country plans to conduct more satellite launches, which outside governments see as a cover for banned tests of missile technologies.

On Monday, Kim told the U.N. General Assembly's disarmament committee that the situation on the Korean Peninsula had "reached the touch-and-go point and a nuclear war may break out any moment," citing the U.S.-South Korea drills and what he called U.S. plans to remove North Korea's leadership. He said the North has the right to possess nuclear weapons in self-defense.