BEIJING (AFP) – China is due on Thursday (Aug 4) to kick off its largest-ever military exercises encircling Taiwan, in a show of force straddling vital international shipping lanes following a visit to the self-ruled island by US House Speaker Nancy Pelosi.

Mrs Pelosi left Taiwan Wednesday after a less than 24-hour visit that defied a series of increasingly stark threats from Beijing, which views the island as its territory.

The House speaker, second in line to the presidency, was the highest-profile elected US official to visit Taiwan in 25 years.

She declared her presence made it “unequivocally clear” that the United States would “not abandon” a democratic ally like Taiwan.

Her trip sparked a furious reaction from Beijing, which vowed “punishment” for those that had offended it and announced military drills in the seas around Taiwan – some of the world’s busiest waterways.

China’s Taiwan affairs office said on Thursday punishment of pro-Taiwan independence diehards and external forces was reasonable and lawful.

Taiwan is not a regional issue but China’s internal affair, the Beijing-based office added, as the country’s military embarks on targeted military drills in a number of zones surrounding the island.

The exercises, set to begin at noon (0400 GMT), will involve “training activities including live-fire drills”, according to an announcement in state media.

They will take place in multiple zones encircling Taiwan – at some points within just 15km of the island’s shore – and will conclude at midday on Sunday.

Nationalist state-run tabloid the Global Times reported, citing military analysts, that the exercises were “unprecedented” and that missiles would fly over Taiwan for the first time.

“This is the first time the PLA will launch live long-range artillery across the Taiwan Straits,” the newspaper said, referring to China’s military, the People’s Liberation Army.

Drills taking place since last Tuesday have set the stage for the exercises, with Beijing’s Xinhua news agency reporting they had simulated a “joint blockade” of Taiwan.

Taipei has condemned the plans, warning they threaten the security of the East Asia region.

“Some of the areas of China’s drills breach into… (Taiwan’s) territorial waters,” defence ministry spokesman Sun Li-fang said at a press conference Wednesday.

“This is an irrational move to challenge the international order.”

Taiwan’s defence ministry said on Thursday its website suffered cyber attacks and went offline temporarily, adding it was working closely with other authorities to enhance cyber security as tensions with China rise.

The government urged the island’s companies to enhance their cybersecurity in the coming days.

Earlier this week, several government websites, including the presidential office, were subject to overseas cyber attacks, some of which authorities said were launched by China and Russia.