US Secretary of State Antony Blinken will meet China's top envoy and potentially President Xi Jinping Monday, on the final day of a trip to Beijing aimed at improving severely strained ties.

The top US diplomat met for seven and a half hours on Sunday with Foreign Minister Qin Gang, more than expected, with the two sides agreeing to keep up communication as they look to avoid conflict.

Neither side has confirmed a meeting between Blinken and Xi, China's most powerful leader in decades, whose meeting with President Joe Biden in November in Bali raised cautious hopes for a thaw in the relationship.

But diplomats see a meeting likely with Xi.

Blinken is scheduled to first meet with China's top diplomat, Wang Yi, whose position in the Communist Party ranks above the foreign minister.

Tensions have soared between the world's two largest economies in recent years on issues ranging from trade to technology to Taiwan.

US officials say that they do not expect major breakthroughs from Blinken's talks but they hope to reopen regular lines of communication to prevent mishaps from escalating into major conflict.

Both countries said Sunday that Qin accepted an offer to pay a return visit to Washington at a later date.

The talks on Sunday, including a banquet dinner at the state guesthouse in the Diaoyutai gardens, were "candid, substantive and constructive", State Department spokesman Matthew Miller said.

Blinken stressed "the importance of diplomacy and maintaining open channels of communication across the full range of issues to reduce the risk of misperception and miscalculation", Miller said.

Behind closed doors, Qin told Blinken that relations between the United States and China "are at the lowest point since the establishment of diplomatic relations", according to state-run broadcaster CCTV.

"This does not conform to the fundamental interests of the two peoples, nor does it meet the common expectations of the international community," Qin said during the talks at the ancient Diaoyutai gardens.

But he issued a warning on Taiwan, the self-ruling democracy claimed by Beijing, which has launched live-fire military drills twice near the island since August in anger over actions by top US lawmakers.

"The Taiwan issue is the core of China's core interests, the most important issue in China-US relations and the most prominent risk," Qin said.

A senior US official, speaking on condition of anonymity, said the discussions went beyond the usual talking points, including on Taiwan.

"This was a real conversation," he said.

Xi last week struck a conciliatory note as he met another prominent American, software tycoon turned philanthropist Bill Gates.

"You are the first American friend I have met in Beijing this year," Xi told Gates in Beijing, according to the state-run People's Daily. 

"We have always placed our hopes on the American people, and hoped for continued friendship between the peoples of the two countries," he added.

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