Chinese President Xi Jinping is expected to press US President Donald Trump over a pending $14 billion American arms package for Taiwan when the two leaders meet in Washington on Thursday.

Last week, Beijing is believed to have warned Washington that it would call off the summit if the US approved the deal, which has been in limbo for months.

At their last meeting, in Beijing in May, Xi told Trump that the Taiwan question was the most important issue in relations between their countries and that mishandling it would put ties "in great jeopardy". By all accounts, the Taiwan question is expected to weigh heavily on Thursday's talks as well.

The package includes air defence missiles and surface-to-air missile systems. If approved, it would be the largest US arms sale to Taiwan, surpassing a separate $11 billion package cleared in December last year. Washington put the new tranche on hold to make sure it had enough supplies for its war with Iran.

"China's objective is to hold the US to the 1982 US-China Joint Communique that calls on Washington to gradually reduce weapons sales to Taiwan," said Manoj Joshi, a distinguished fellow at the Observer Research Foundation, a Delhi-based think tank.

The People's Republic of China, as the mainland state is formally known, regards Taiwan as a breakaway region and has vowed to bring it under its control. In his New Year's message this year, Xi said the "reunification of our motherland, a trend of the times, is unstoppable".

Taiwan sees itself as an independent country, with its own constitution and elected leaders. Only 12 states, including the Vatican, recognise it.

Across the three documents, the US acknowledged the Chinese position that there is one China, pledged not to interfere in China's internal affairs, backed a peaceful resolution of the Taiwan question and said it would gradually reduce arms sales to Taiwan. But, in a memo accompanying the 1982 communiqué, then-US President Ronald Reagan said US willingness to reduce arms sales was “conditioned absolutely upon the continued commitment of China to the peaceful solution” of differences with Taiwan.

Alongside the communiqués, the US Congress passed the Taiwan Relations Act in 1979, which set up an unofficial relationship with Taiwan and promised that the US "shall provide Taiwan with arms of a defensive character”. In 1982, Washington also gave Taiwan what are now called the 'Six Assurances'. Among them, the US said it would not set a date for ending arms sales to Taiwan, would not alter its position on Taiwan's sovereignty and would not formally recognise Chinese sovereignty over the island.

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First, he said, "Taiwan is located at a critical node within the first island chain, anchoring a network of US allies and partners — stretching from the Japanese archipelago down to the Philippines and into the South China Sea — that is critical to the region's security and critical to the defence of vital US interests in the Indo-Pacific."

Second, "geographically, Taiwan is also situated alongside major trade lanes that provide sea lines of communication for much of the world's commerce and energy shipping".

Third, "Taiwan is a beacon of democratic values and ideals. In stark contrast to deepening authoritarianism and oppression in the PRC, Taiwan has proven the possibilities of an alternative path to that of the Chinese Communist Party."

Taiwan also matters for its chips. The island produces most of the advanced semiconductors, with the Taiwan Semiconductor Manufacturing Company (TSMC) – the world's largest contract chipmaker – supplying companies the likes of Apple and Nvidia.

A US-China conflict over Taiwan could severely curtail global access to chips used in cars, planes, artificial intelligence data centres and smartphones, Bloomberg Economics said in a February analysis. It put the cost of that scenario, the most extreme of five it modelled, at about $10.6 trillion, roughly 9.6% of global GDP, in the first year alone.

On Monday, US secretary of state Marco Rubio and his counterparts from Japan and South Korea stressed the importance of peace and stability across the Taiwan Strait and "expressed support for Taiwan's meaningful participation in appropriate international organisations". In a joint statement after the meeting, they said they stand "against economic coercion and non-market policies and practices" and "arbitrary export restrictions that disrupt supply chains", in what appeared to be a reference to China.

Also read: Looking beyond the Trump-Xi meeting in Washington

"In May, Trump called it a 'very good negotiating chip'. So he may use it to extract some concessions from China. But it works the other way as well; it can be used by China to delay the package further," Joshi said.

The question gained significance after reports said Trump wanted to push the deal back to 2028 or 2029, towards the end of his term. In a rare gesture, Trump is also expected to greet Xi at the airport when he reaches the US on Wednesday.

Joshi played down the welcome. "The US has said that the reception would be based on reciprocity, yet they are planning to give Xi a flypast and an obviously grand reception. But it is purely a reciprocal gesture and not some concession," he said.

For now, there is little sign of a major breakthrough. "The agenda plate is quite full," Joshi said, pointing to the terms of a US-China dialogue on AI, which the two sides have yet to work out, and to the tariff truce agreed last October, which runs out on November 10 and needs renewal. He also cited the new Russia sanctions legislation, which seeks to punish countries such as China and India for trading oil with Moscow. "This is not an automatic tariff but can be used by Trump to negotiate concessions," Joshi said. He added that the two sides are also trying to deepen military-to-military dialogue to keep ties stable, and that the US wants to remind China its promised purchases of American farm goods are behind schedule.