President Yoon Suk Yeol, US President Joe Biden and Japanese Prime Minister Fumio Kishida plan to adopt a trilateral summit document stipulating a "duty to consult" with one another in the event of a crisis, a senior US official has said.

The leaders are poised to issue the document during a landmark three-way summit at the Camp David presidential retreat in Maryland on Friday, the official said, in a sign of deepening solidarity amid North Korea's military threats, China's assertiveness and Russia's war in Ukraine.

The envisioned commitment to consult fueled speculation that the three countries are on course to elevate their cooperation closer to a level approximating an alliance, but it remains to be seen whether the word, "duty," will make it into the finalized document, observers said.

"All three leaders will take a pledge (on) what we would call a duty to consult in the event of a crisis or a set of circumstances that affects the security of any one of our countries," the official said in a telephonic press briefing Thursday.

Yoon, Biden and Kishida will also agree that their countries will hold a trilateral summit "on an annual basis" and take steps to build a "state-of-the-art" three-way hotline, through which "we can engage in moments of crisis and uncertainty," the official said.

Another U.S. administration official said the consultation commitment will be contained in a stand-alone statement, noting it will take "our security and broader coordination to the next level in a really fundamental way."

"What it very much is is a commitment amongst our three countries that if there is a regional contingency or a threat, we will immediately and swiftly consult with one another," the official said. "We will discuss ways to share information to align our messaging and to take policy actions in tandem with one another."

The official described the consultation commitment as part of efforts to build a "common security" platform, dismissing the notion that it could amount to a formal alliance commitment.

"What we are building here is a common security framework that increasingly gives our leaders and our top national security officials the incentive to work closely together whenever one of us faces a challenge and to make sure that not only the challenging picture but the policy options that follow are taken together," the official said.

The official added that the commitment "does not infringe upon any one of our country's rights to defend itself under international law, nor does it change or impinge in any way on the existing bilateral treaty commitments between South Korea and the US, and between the US and Japan."

New headway in the US' push for trilateral cooperation has unnerved China. In a recent op-ed piece, the Global Times, China's nationalist outlet, criticized a "US desire to build a mini-NATO-style trilateral military alliance in Northeast Asia."

But a U.S. administration official said the Camp David summit is not about taking steps to isolate China.

"I would suggest that what you're seeing in Japan, South Korea and the U.S. is largely a response to security steps and measures that we believe are antithetical to our interests," the official said. "Three countries are committed to an effective, practical diplomacy with China."

US officials indicated the trilateral summit will produce at least three separate documents -- a statement on the duty to consult, one on the principles of three-way engagement and an overarching document of purpose.

The document on the basic principles of engagement will "demonstrate that it is not a single summit among these three leaders but that they are building something that they intend to pass on to subsequent administrations," the second administration official said, adding the trilateral summit will mark the "beginning of a new chapter in our partnership."

"I think our goal will be to lock in trilateral engagement that will make it difficult to backtrack from the commitments that each of the three will make at Camp David, and again, I think it's nothing short of historic," an official said.

Asked if the three-way hotline and duty to consult will be activated in the event of a potential Chinese attack on Taiwan, one administration official refused to give a direct answer.

"I think that the discussions that we've undertaken between the three countries involve the security and political situations in the broader Indo-Pacific," the official said. "There will be language tomorrow in our joint statement that reaffirms and underscores our commitment to the maintenance of peace and stability across the (Taiwan) strait."

On China's assertiveness in the South China Sea, a White House official said that there will be "some robust language" in a statement on the three sides' "common" position based on "international law" and "opposition to coercion and militarization."

"I don't think I've ever been involved in a series of preparations in which the alignment between the three governments was so clear and straightforward," the official said. "I believe this alignment and this shared sense of both threat perception, opportunities and duty will be on full display."

One of the officials also underscored the significance of the venue for the trilateral summit.

"Camp David was chosen quite carefully. I think there's a recognition that that venue is reserved for only the most important and significant such meetings," the official said.

The White House said earlier that Yoon and Kishida will be the first foreign leaders to be invited to Camp David under the Biden administration, as well as since 2015.

Friday's event will begin with the arrival of Yoon and Kishida at the U.S. presidential retreat on separate U.S. Marine helicopters provided by the White House.

Biden will hold bilateral talks with Yoon and Kishida before holding a three-way summit and a joint conference with his South Korean and Japanese counterparts, according to the officials.