President Xi Jinping has told his American counterpart Donald Trump that US-China ties have been "affected by some negative factors", an allusion to a series of US actions in the past week slammed by Beijing.
Mr Trump called Mr Xi and Japan's Prime Minister Shinzo Abe separately on Sunday night, with the phone calls focused on the threat North Korea's nuclear ambitions pose to regional peace.
Mr Xi said during the call that Sino-US ties "have achieved important results" since the two leaders met in Florida in April. But he also said the relations have been "affected by some negative factors".
China's Defence Ministry yesterday slammed the United States for seriously damaging peace and stability in the South China Sea after an American warship sailed near an island in the Paracels claimed by China. The Chinese Foreign Ministry called the US move a "serious political and military provocation".
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Mr Xi also urged Mr Trump to abide by Washington's "one China" policy, and "properly handle the Taiwan-related issues in accordance with the one-China principle".
The reference to Taiwan has to do with last Thursday's announcement that the US would sell US$1.42 billion (S$2 billion) worth of weapons to the island, which China regards as a breakaway province.
This followed Wednesday's proposal by a US Senate panel to let US warships call at Taiwan's ports.
Taiwan aside, a series of actions by the Trump administration has also irritated China. These include fresh sanctions by the US Treasury Department on a Chinese bank accused of laundering North Korean money, and a State Department report that put China on a list of the world's worst human-trafficking offenders.
The US State Department also expressed concern about Beijing's respect for freedoms in Hong Kong on the 20th anniversary of the city's return to China last Saturday.
Experts said that while the US- China relationship seemed to have entered a honeymoon period after the Florida meeting, events of the past week and Sunday's phone conversation showed numerous problem areas continued to hamper ties.
"Based on how the two leaders interacted when they met in Florida, many on both sides were optimistic that ties were on an upward trend," said Professor Jia Qingguo, dean of the School of International Studies at Peking University. "These preliminary assessments were optimistic because expectations were low for the Mar-a-Lago meeting, and US-China ties are now simply returning to a normal state of affairs."
Another Sino-US expert, Professor Shen Dingli of Fudan University, said that this "good cop, bad cop routine" was part of Mr Trump's negotiating tactics to get China to do more to rein in North Korea, but that Beijing was unlikely to bite.
Asked by reporters if the honeymoon had indeed ended, Foreign Ministry spokesman Lu Kang said "neither China nor US officials have ever used this (concept)".
"For China, we wish to further develop Sino-US ties on a nonconfrontational, mutually respectful and win-win basis, to expand our common ground while managing our differences," he told a regular press briefing yesterday.
"For two large countries like ours, it is unavoidable for issues relating to bilateral ties to crop up from time to time."
But he said that both China and the US have the determination and will to seek progress in the development of their ties.