China and the United States are refusing to budge over Beijing's assertive development in disputed parts of the South China Sea.
Chinese officials are politely but pointedly dismissing Washington's push for US-proposed ways to ease tensions.
As US Secretary of State John Kerry wrapped up a visit to China today, both sides stressed the importance of dialogue to resolve competing claims in the waterway.
But neither showed any sign of giving ground over Chinese land reclamation projects that have alarmed the United States and China's smaller neighbours.
Kerry was today meeting Chinese President Xi Jinping before heading to South Korea to complete a short Asian tour that has been clouded so far by concerns over China's construction in the South China Sea.
The US and most members of the Association of Southeast Asian Nations want a halt to the projects, which they suspect are aimed at building islands and other land features over which China can claim sovereignty.
"We are concerned about the pace and scope of China's land reclamation in the South China Sea," Mr Kerry said yesterday.
He urged China to speed up talks with ASEAN on guidelines for handling maritime activity in disputed areas.
Mr Kerry said the goal is to help "reduce tensions and increase the prospect of diplomatic solutions.
"I think we agree that the region needs smart diplomacy in order to conclude the ASEAN-China code of conduct and not outposts and military strips."
Chinese foreign minister Wang Yi indicated that while China was prepared to talk, it would not back down on the construction that, he said, "is something that falls fully within the scope of China's sovereignty.
"The determination of the Chinese side to safeguard our own sovereignty and territorial integrity is as firm as a rock, and it is unshakable.
"It has always been our view that we need to find appropriate solutions to the issues we have through communications and negotiations that we have among the parties directly concerned with peaceful and diplomatic means on the basis of respecting historical facts and international norms. This position will remain unchanged in the future."
He added that the differences between China and the US could be managed "as long as we can avoid misunderstanding and, even more importantly, avoid miscalculation".
The Chinese claims and land reclamation projects have unsettled the region where South China Sea islands and reefs are contested by China and five other Asian governments.
These activities have led to maritime clashes, accompanied by nationalistic protests and serious diplomatic rows.
The US says it takes no position on the sovereignty claims but insists they must be negotiated. Washington also says ensuring maritime safety and access to some of the world's busiest commercial shipping routes is a national security priority.
China has bristled at what it sees as US interference in the region and wants to negotiate with the ASEAN countries individually, something those much smaller nations fear will not be fair.
In one disputed area, the Spratly Islands, US officials say China has reclaimed about 2,000 acres of dry land since 2014 that could be used as airstrips or for military purposes. The US argues that man-made constructions cannot be used to claim sovereignty.
Obama administration officials have declined to comment on reports that it may deploy military assets, or is considering a demonstration of freedom of navigation within 12 nautical miles of the islands' notional territorial zone.
But they have said many of the features claimed by China in the disputed Spratlys are submerged and do not carry territorial rights, and maintained that China cannot "manufacture sovereignty" with its reclamation projects.
Despite the clear disagreements over the South China Sea, Mr Kerry and Mr Wang said they were on track to make progress in other areas.
They included climate change, the fight against violent extremism, and preparations for the next round of the US-China strategic and economic dialogue in June and Mr Xi's visit to Washington in September.
They expressed pleasure with their co-operation in the Iran nuclear talks, their solidarity in trying to denuclearise North Korea and combat diseases such as the deadly Ebola virus.