Taiwan’s new president has formally labelled China a “foreign hostile force” and ramped up national security measures in the face of growing threats and a string of spying cases.

The new measures announced on Thursday include a controversial proposal to restore a military court system in Taiwan, which was under martial law until the late 1980s.

The president, Lai Ching-te, made the announcement after convening a high-level national security meeting. It prompted an almost immediate reaction from Beijing, which called Lai a “destroyer of cross-Straits peace” and “creator of crisis” who was pushing Taiwan towards the “perilous brink of war”.

Lai told reporters he was responding to China’s increasing grey zone attacks and infiltration of government, military and society. He said China met the definition of a “foreign hostile force” under Taiwan’s anti-infiltration act and he had “no choice but to take even more proactive measures”.

“China has been taking advantage of democratic Taiwan’s freedom, diversity, and openness to recruit gangs, the media, commentators, political parties, and even active-duty and retired members of the armed forces and police to carry out actions to divide, destroy, and subvert us from within,” Lai said.

The most concrete measure announced was plans to re-establish a peacetime military court system to prosecute “military crimes as sedition, aiding the enemy, leaking confidential information, dereliction of duty, or disobedience”.

Taiwan was ruled under brutal martial law for decades, and abolished its military court in 2014 after backlash over the handling of an investigation into the hazing-related death of a young recruit.

Opposition parties – which hold the majority in Taiwan’s legislature and have been highly obstructionist to Lai’s agenda – have questioned the plan. Opposition KMT legislator Wang Hung-wei said her party wasn’t “totally against it” but accused the ruling DPP of backflipping on its long-held positions. Another opposition party, the TPP, said the proposal would send Taiwan backwards on human rights.

In his speech Lai flagged tightening restrictions on Chinese travellers and new residents, as well as monitoring of Taiwanese people working or travelling in China.

Taiwan has prosecuted dozens of current and former military personnel who have been recruited as spies for Beijing, and has criticised Taiwanese entertainers and influencers for endorsing Beijing’s claims over Taiwan and spreading propaganda, Lai said.

This week a Chinese-born resident was expelled for posting online content endorsing a Chinese invasion. China has also been offering an unknown number of Taiwanese citizens Chinese residency or passports, which Lai said was “an attempt to muddle Taiwanese people’s sense of national identity”.

China’s government this week concluded its annual Two Sessions political meeting, during which officials emphasised their continued objective to annex Taiwan and punish leaders it sees as “separatists”. Officials at the Two Sessions reiterated a preference for peaceful “reunification”, but hardened language around a willingness to use military force if necessary.

Chen Binhua, spokesperson for China’s Taiwan Affairs Office, had said on Wednesday: “If the ‘Taiwan independence’ separatist forces provoke, exert pressure, or dare to cross the red line, resolute actions will be taken in response.”

On Friday morning Taiwan’s defence ministry said 12 fighter jets, seven navy vessels and one “official” ship (likely coast guard) had been detected around Taiwan since 6am. It said nine of the jets crossed the median line of the Taiwan Strait.

Additional research by Jason Tzu Kuan Lu