China has been patrolling the waters around Taiwan with its newest attack submarines carrying supersonic missiles.
The Type-039C Yuans, that was only commissioned in July, have been deployed in China’s East Sea Fleet and is the cutting edge of the country’s non-nuclear submarines.
It comes as Taiwan accused China of exaggeration and "tricks" on Tuesday after the Chinese military published footage of the strategically located Penghu islands where there is a major Taiwanese air base.
And China has imposed sanctions on seven Taiwanese officials and lawmakers it accused of being "independence diehards".
China, which claims Taiwan as its territory, has carried out military exercises around the island this month after a visit by US House of Representatives Speaker Nancy Pelosi, who was followed by five US lawmakers on Sunday and Monday.
The Chinese military unit responsible for the area adjacent to Taiwan, the People's Liberation Army's Eastern Theatre Command, released on Monday video of the Penghu islands, apparently taken by a Chinese air force aircraft close by.
Taiwan Air Force Vice Chief of Staff for Operations Tung Pei-lun told reporters in Taipei that this was Chinese information warfare, though he said he had no comment on who had taken the video.
"China used the exaggerated tricks of cognitive warfare to show how close it was to Penghu - which is not true," Tung said.
Taiwan's Defence Ministry on Monday, in an update of Chinese air force activity near Taiwan, showed on a map that the closest Chinese aircraft to Penghu that day were four J-16 fighters.
The fighters crossed the Taiwan Strait median line - normally an unofficial barrier between the two sides - but stayed closer to the Chinese coast than Penghu, the map showed.
Tung said Taiwan had a real-time "grasp" of what was going on in the skies, and that Chinese aircraft have been operating to the north and southwest of Taiwan and across the median line.
Penghu is close to Taiwan's southwestern coast, unlike the Taiwan-controlled Kinmen and Matsu islands which are right next to the Chinese coast. Penghu is a popular summer tourist destination for its beaches, reefs and seafood.
China's Taiwan Affairs Office said among those sanctioned were Taiwan's de facto ambassador to the United States, Hsiao Bi-khim, Secretary-General of Taiwan's National Security Council Wellington Koo, and politicians from Taiwan's ruling Democratic Progressive Party.
A Taiwan Affairs Office spokesperson said that those sanctioned would not be able to visit China, Hong Kong and Macau. Firms and investors related to them will also not be allowed to profit in China.
"For some time, a few diehard separatist elements, out of their own interests, have gone to lengths to collude with external forces in provocations advocating Taiwan independence," state news agency Xinhua cited the spokesperson as saying.
"They have deliberately instigated confrontations across the Taiwan Strait, and recklessly undermined peace and stability in the region."
Taiwan's foreign ministry said in response that the island was a democracy that "could not be interfered with by China".
"Even more, we cannot accept threats and menace from authoritarian and totalitarian systems," ministry spokesperson Joanne Ou told reporters in Taipei.
The sanctions will have little practical impact as senior Taiwanese officials do not visit China.
