President Donald Trump raised eyebrows when he told his Vietnamese counterpart Tran Dai Quang he could mediate in the South China Sea dispute .

"If I can help mediate or arbitrate, please let me know," he said. "I'm a very good mediator and arbitrator."

But the offer, made on Sunday (Nov 12) during the American leader's state visit to Hanoi, was largely dismissed by analysts and politely set aside by regional diplomats.

Hanoi-based analyst Ha Hoang Hop called it a "spontaneous" comment. "There is no way, no legal or even political basis for the US and Trump to do this," said the chairman of consultancy firm Think Tank Viet Know.

While Americans are not claimants in the strategic waterway, they have been accused by China of interfering in the dispute by bolstering the maritime capabilities of Vietnam, one of several rival claimants.

Mr Trump's visit to the Vietnamese capital over the weekend was followed mere hours later by the arrival of Chinese President Xi Jinping.

Hanoi was careful to welcome each leader equally lavishly - with banquets, military bands and rows of flag-waving children.

Analysts note there were no surprises in the joint statement Vietnam issued with the US, where both sides pledged to deepen trade and investment, as well as defence cooperation and people-to-people ties.

Ms Phuong Nguyen, an adjunct fellow with the Centre for Strategic and International Studies, said: "The Vietnamese saw it as a way to get clarity on US policy in Vietnam. And they got a reaffirmation that the more things change, the more things stay the same."

Vietnam, attuned to Mr Trump's need to tout the economic success of his trip, also foregrounded the US$12-billion (S$16 billion) commercial deals signed in his presence.

Mr Xi's visit, in contrast, "was a formal reset in the China-Vietnam relationship", said Ms Phuong. "It allowed both communist parties to frame the bilateral relationship as broader and substantive, outside the South China Sea issue."

While the communist neighbours signed cooperation pacts on wide-ranging areas like border control, renewable energy and banking, the South China Sea issue was also discussed.

According to Nhan Dan, the mouthpiece of Vietnam's communist party, party general-secretary Nguyen Phu Trong proposed to Mr Xi on Sunday that both countries adhere to the existing Declaration of Conduct in the disputed waters, while hold "practical negotiation for the building of an effective and efficient" Code of Conduct, which is more binding.

China and Asean adopted a negotiating framework for a code of conduct in August, though many expect a comprehensive agreement to take much longer. Besides China and Vietnam, Brunei, Malaysia, the Philippines and Taiwan also have claims in the disputed waters.

On Monday, China's state media agency Xinhua reported that both countries "reached an important consensus... to appropriately manage maritime issues, steadily advance all forms of maritime cooperation, including joint development and jointly strive to uphold peace and stability in the South China Sea."

Dr Hop said: "Both sides are trying to manage their differences to avoid any risk or tension."