If China's claims on Taiwan are about territorial integrity then it should also take back land from Russia signed over by the last Chinese dynasty in the 19th century, Taiwan President Lai Ching-te said in an interview with Taiwanese media.
China views democratically governed Taiwan as its own territory and has never renounced the use of force to bring the island under its control. Taiwan's government rejects those claims, saying only the island's people can decide their future.
Speaking in an interview with a Taiwanese television station broadcast late on Sunday, Lai, who China calls a "separatist", brought up the 1858 Treaty of Aigun in which China signed over a vast tract of land in what is now Russia's far east to the Russian empire, forming much of the present day border along the Amur River.
China's Qing dynasty, then in terminal decline, originally refused to ratify the treaty but it was affirmed two years later in the Convention of Peking, one of what China refers to as the "unequal" treaties with foreign powers in the 19th Century.
"China's intention to attack and annex Taiwan is not because of what any one person or political party in Taiwan says or does. It is not for the sake of territorial integrity that China wants to annex Taiwan," Lai said.
"If it is for the sake of territorial integrity, why doesn't it take back the lands occupied by Russia that were signed over in the Treaty of Aigun? Russia is now at its weakest right?" he added.
"The Treaty of Aigun signed during the Qing - you can ask Russia (for the land back) but you don't. So it's obvious they don't want to invade Taiwan for territorial reasons."
China's Taiwan Affairs Office did not immediately respond to a request for comment. China's government says Taiwan has been Chinese territory since ancient times.
The Qing signed over Taiwan to Japan in 1895 in another "unequal" treaty, and in 1945 at the end of World War Two it was handed over to the Republic of China government, which four years later fled to Taiwan after losing a civil war with Mao Zedong's communists.
Lai said that what China really wants to do with its designs on Taiwan is to change the rules-based international order.
"It wants to achieve hegemony in the international area, in the Western Pacific - that is it's real aim."
