The Chinese mainland resolutely opposes any exchanges between militaries or government officials of the United States and Taiwan, a Chinese mainland spokesman said on Wednesday.

An Fengshan, spokesman for the Taiwan Affairs Office of the State Council, said in response to a recent speech by a Chinese diplomat reiterating that matters involving Taiwan are internal Chinese affairs.

"The day that a US Navy vessel arrives in Kaohsiung is the day that our People's Liberation Army unifies Taiwan with military force," Li Kexin, minister counsellor at the Chinese Embassy in the US, said at an embassy event in Washington on Tuesday.

He also said that China would activate its Anti-Secession Law if the US sent warships to Taiwan.

Li's speech stirred heated discussion on the island, with Taiwan media describing it as the "red line" of unification by force.

"Any attempt to undermine the country's sovereignty and territorial integrity is bound to incur the Chinese people's opposition and will not succeed," An said.

He also said the mainland opposes any "Taiwan independence" activities, including public voting.

The mainland will uphold peaceful reunification and the "one country, two systems" principle; and it will promote the peaceful development of cross-Straits relations, according to the Ministry of Foreign Affairs at a news conference earlier this week.

Beijing urged the United States to abide by the one-China policy and the three China-US joint communiques, and cautiously and properly handle the Taiwan issue.

"One country, two systems" and peaceful reunification are the major principles at the heart of Taiwan issues, and peaceful development is the way forward, said Liu Xiangping, professor of Taiwan studies at Nanjing University in Jiangsu province.

Li's speech, he said, was the result of Taiwan's Democratic Progressive Party recently attempting to bring US forces to Taiwan to back up the notion of "independence". Some forces in the US－especially in the military－that still hold a Cold War mindset and are attempting to use Taiwan as leverage to obstruct China's peaceful rise, he added.

Li's speech was based on the premise of a US warship's arrival in Taiwan, which would violate the three Sino-US joint communiques, Liu added. The communiques state that the US recognizes one China and would gradually reduce and eventually stop arms sales to Taiwan.

"If the US were to violate the communique, it would violate international law …and China would respond intensely," Liu said.

"If Taiwan authorities violate the law to sabotage the status quo, leading to the deterioration of cross-Straits relations, they should swallow the bitter result and be aware of the wrong they've committed," Liu said.

Xinhua contributed to this story.