The commitment of the US to Taiwan is "rock-solid", the State Department confirmed at the weekend, as it warned that China's "attempts to intimidate" the island are a threat to regional peace. Meanwhile, France has upgraded its presence in Taiwan, and will take part in joint US-Japanese exercises in the East China Sea in May.
For the second day in a row, mainland Chinese air force planes including 12 fighter jets entered Taiwan's air defence identification zone (Adiz) on Sunday.
China regards the island of Taiwan as an inseparable part of its own territory, and asks all countries which recognise Beijing diplomatically to regard Taiwan as China's province.
Most countries maintain 'commercial' or 'trade' offices in Taipei, often manned by professional diplomats. China has lived with the status quo since Nationalist troops fled to the island after the Communist revolution in 1949.
China's activities over the weekend mark a ratcheting up of pressure, with fighters and bombers rather than reconnaissance aircraft being dispatched, as has been the case in recent months.
After eight Chinese bomber planes and four fighter jets flew into Taiwan's defence zone on Saturday, between mainland Taiwan and the Taiwan-controlled Pratas Islands in the South China Sea, a further 15 flew into the same air space on Sunday, Taiwan said.
Taiwan's Defence Ministry said China sent six J-10 fighters, four J-16s, two SU-30s, a Y-8 reconnaissance aircraft and two Y-8 anti-submarine aircraft.
Taiwan's air force was mobilised in response to the Chinese incursions, it added.
The move is likely to further concern in Washington. Joe Biden has already urged China to stop pressuring Taiwan and reaffirmed US commitment to the island and desire to deepen ties.
When the US severed ties with Taipei in 1979 and recognised Beijing, it maintained an open door to Taiwan through the Taiwan Relations Act, under which Washington promises to help Taiwan to "maintain a sufficient self-defense capability,'' which is supported by yearly arms sales to the island, including anti-aircraft missiles, F-16s and frigates.
Beijing is fiercely critical at any official contacts with Taiwan and tries to keep the island diplomatically isolated. Currently Taiwan maintains official diplomatic ties with only 15 countries - mainly tiny islands in the Pacific, some Latin American countries and the Vatican.
President Donald Trump embraced warmer ties with the island as he feuded with China on issues like trade and national security.
Beijing has called for a reset in US-China ties under Biden and on Thursday warned the US to "cautiously and appropriately handle Taiwan issues to prevent harm to US-China relations".
But the new US president is expected to remain tough on the superpower rival despite a softening of diplomatic tone.
France is at guard
Meanwhile, France, which established diplomatic relations with mainland China in 1964, slightly upgraded 'informal' cooperation with Taiwan last week.
Taiwan's press noted that the Mayor of Taiwan's second largest city Kaohsiung, Chen Chi-mai, and French Office in Taipei Director Jean-Francois Casabonne-Masonnave, have signed an agreement to promote cooperation on virtual reality development, facilitating for instance virtual tours in the Louvre Museum.
The step is symbolic, but shows France is maintaining a keen interest in the island.
A more significant gesture is the announcement that France will take part in joint military exercises with the US and Japan in the East China Sea in May this year.
The exercises, first reported by Japan's Sankei Shibun newspaper, to be conducted on one of Japan's uninhabited outlying islands, will focus on providing relief efforts during a natural disaster, but could also form the basis for a defence against military attack, the paper suggested.
Reuter's news agency reports that Japan's defence ministry was not immediately available to respond to its request for confirmation.
The joint exercises aim to counter China, which claims Japanese-controlled islands in the East China Sea, according to Sankei.
"We want to demonstrate our presence to the region and send a message about Japan-France cooperation," Admiral Pierre Vandier, chief-of-staff of the French navy, told Sankei in a separate interview when he paid a visit to Japan last November.
Vandier, who was appointed France's navy chief in November, has expressed 'concern' about China's 'conquering mentality' in an interview with AFP, warning about the 'rapid expansion' of China's navy.
Zhang Junshe, a senior research fellow at the PLA Naval Military Studies Research Institute retorted in China's hardline Global Times that while France "wants to show its loyalty to Washington," Paris should evaluate the forces involved, adding that "China is no longer a country that can easily be bullied.
"The days are also long gone when Western aggressors could occupy a country for hundreds of years by simply setting up a few cannons on a coast in the East," writes Zhang.
(With AP, AFP, Reuters)