'Pro-independence forces have never stopped their activities for a single minute. Combatting and containing those forces remains the first priority for compatriots from both sides,' said Mr Jia, who is also chairman of the Chinese People's Political Consultative Conference.
He warned that the public should be on guard against attempts by pro-independence politicians to seek independence through changes to the island's constitution.
The celebrations, which sought to play up the island's historical connection to the mainland, were the first time that Beijing had officially marked 'Taiwan Retrocession Day', when the island was handed over to Chinese rule by Japan after its defeat in 1945.
'The return of Taiwan to China is undeniable, and the legal status of Taiwan as an inalienable part of China's territory is beyond doubt, and can never be challenged,' Mr Jia said.
The same message was highlighted yesterday in an editorial in the People's Daily.
'As we review the history of Taiwan from its cession to its recovery and other historical facts about Taiwan, we see that Taiwan has never been a country but instead an inalienable part of the Chinese territory,' the editorial said.
In his speech, Mr Jia renewed Beijing's calls for reunification, urging Taipei to recognise the one-China principle and the so-called 1992 consensus, which Beijing saw as the prerequisite for any political dialogue between the two sides.
'We do not have any prejudice over which individual or political party [in Taiwan] conducts dialogue and negotiations. Compatriots on both sides are Chinese and negotiations will be on an equal footing,' Mr Jia said.
President Hu Jintao has adopted a softer approach in dealing with Taiwan. He has met opposition leaders from the island and offered economic concessions to woo support from Taiwanese businessmen and the public.
However, the island's government under President Chen Shui-bian has remained unmoved and has continued to discourage closer contacts with the mainland.
In his speech yesterday, Mr Jia made only a veiled reference to 'foreign influence' and chastised Taiwanese politicians who favoured forging an alliance with Japan over reunification with the mainland.
Among other activities marking the anniversary, a photographic exhibition opened at the National Museum and a gala was being held in Beijing.
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