While China has worked hard to get Trump to understand the importance of Taiwan to the China-U.S. relationship, it has never seriously expected Washington to stop selling it weapons, provision for which is explicitly made in U.S. law. The ministry called it damaging to Chinese sovereignty.
This week, the United States imposed sanctions on two Chinese citizens and a shipping company for helping North Korea's weapons programmes, announced a $1.4 billion arms sale for Taiwan, and said it would like sick Chinese dissident Liu Xiaobo to be treated "elsewhere".
Official confirmation of the arms sale, under consideration since January, coincided with Xi's officiation at an ostentatious military parade in Hong Kong on Friday, celebrating China's reunification with what until 1997 Beijing regarded as a "renegade province" similar to Taiwan.
"Mainland China will not be happy about today's notification, but Taiwan has a right to its self-defense", said Sean King, senior vice president of NY political consultancy Park Strategies.
The move showed that Trump intends to use the move to tell China and other nations that "I'm still the boss", he said.
Both announcements came during Trump's meeting with South Korea's new president Moon Jae-in at the White House.
Many in Taiwan had been wondering whether Trump was sidelining Taiwan to form stronger relations with Beijing, in part to seek its help in pressuring North Korea to end its nuclear weapons program. Taiwan is an inseparable part of China.
Just after winning election, Trump infuriated China by accepting a congratulatory call from Taiwan's Beijing-skeptic president Tsai Ing-wen, smashing decades of diplomatic precedent. "It's a question of how much the two countries will be able to manage these conflicts, whether they can manage them better than the previous administration".
Beijing's "one-China policy" stipulates that countries seeking diplomatic relations with China must break off relations with Taiwan's autonomous government.
The decision, if implemented, could in effect provide a naval base and facilities for U.S. aircraft carriers and destroyers just off the coast of the Chinese mainland.
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It marks the first proposal of an arms sale to Taiwan since Trump took office on January 20. Since Tsai's inauguration, Beijing has gradually chipped away at Taipei's worldwide space and diplomatic allies.
"The timing (of the arms sale proposal) is good politically, because a lot of people say Trump doesn't like Taiwan", said Huang Kwei-bo, associate professor of diplomacy at National Chengchi University in Taipei.
In addition, Tsai thanked the USA government for approving arms sales to Taiwan, the first defense assistance announced by the Trump administration since its inauguration in January. We will continue to enhance our strength and maintain peace.
The package includes technical support for early warning radar, high speed anti-radiation missiles, torpedoes and missile components.
"And all these actions - sanctions against Chinese companies and especially arms sales to Taiwan - will certainly undermine the mutual confidence between the two sides and runs counter to the spirit of the Mar-a-Lago summit", Cui told reporters.
The arms approved by the USA government for sale to Taiwan include torpedoes, technical support for early warning radar, anti-radiation missiles and missile components, officials from the two governments said.
The US is the island's most powerful ally and arms supplier despite having no official relations with Taipei after switching recognition to Beijing in 1979.
Reform of military pensions is expected to be the most hard to negotiate.
"Peace is not a matter of course.", Tsai said. "Whatever should be done, let's do it".
But for James Reilly, professor of global relations at the University of Sydney, "China will be less likely to do anything about North Korea", from now on, due to the sanctions and arms sales.
It transpired his main aim was to persuade Xi to take a tougher line on North Korea.