United States 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 during Mr Trump's state visit to Hanoi, was largely dismissed by analysts and politely set aside by regional observers.

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 the Think Tank Viet Know consultancy.

While the US is not a claimant in the strategic waterway, it has 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 last weekend was followed 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 noted that there were no surprises in the joint statement Vietnam and the US issued. 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."

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

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

Nhan Dan newspaper, the mouthpiece of Vietnam's communist party, said party general secretary Nguyen Phu Trong proposed to Mr Xi on Sunday that both countries adhere to the existing declaration on conduct in the disputed waters, and hold "practical negotiation for the building of an effective and efficient" code of conduct.

China's Xinhua news agency said 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."