Multiple Chinese planes and ships were detected around Taiwan Strait and some of them have crossed the median line, said the defence ministry on Saturday.
"Facing deliberately heightened military threats, Taiwan will not back down. We will... continue to hold the line of defence for democracy," Tsai said at an event with Pelosi in Taipei.
Such technologies are part of a strategy to deter any possible invasion from China, with its huge army and vast superiority in numbers of warplanes, ships and other weaponry.
The routine exchange of prisoners to their respective territories by the police under a 2009 agreement have grown rarer since Ing-wen took office in Taipei, who regards Taiwan as a sovereign nation.
Beijing has ramped up pressure on Taiwan since President Tsai Ing-wen came to power in 2016, as she rejects its stance that the island is part of "one China".
Earlier in November, Taiwan opened a de facto embassy in Lithuania under the name of Taiwanese Representative Office. Lithuania also plans to open a representative office in Taiwan.
Taiwan has been self-ruled since the two sides split during a civil war in 1949, but China considers the island part of its own territory.
Self-governed Taiwan's 23 million people live under the constant threat of invasion by authoritarian China, which views the island as its territory and has vowed to one day seize it, by force if neces
Tsai Ing-wen also firmly rejected Chinese military coercion, a stance driven home by a rare demonstration of Taiwan's defence capabilities in a parade on its National Day.