Chiang Pin-kung (R), chairman of the Taiwan-based Straits Exchange Foundation (SEF), waves to people at the Pudong International Airport in Shanghai April 29, 2009. (Xinhua File Photo/Xing Guangli) Photo Gallery>>>

    TAIPEI, May 6 (Xinhua) -- Taiwan chief negotiator Chiang Pin-kung said here Wednesday he had submitted his resignation as chairman of the Straits Exchange Foundation (SEF), an offer Taiwan leader Ma Ying-jeou said he wouldn't endorse.

    Chiang, who is turning 77 this December, told media on Wednesday morning that he decided to resign because of his "age" and "physical strength."

    He said it was not a sudden decision and he had already delivered his verbal resignation to Ma by the end of last year.

    Ma, however, said on Wednesday that he tried to retain Chiang in his post and has returned his written resignation.

    He said Chiang was very important for cross-straits affairs and would become even more so in the future.

    Chiang, a Ph.D from the University of Tokyo, was designated as chairman of the Taiwan-based SEF, a non-governmental organization dealing with cross-straits affairs, after Ma became the leader of Taiwan in May 2008.

    As the chief negotiator from Taiwan, he had held rounds of talks with his counterpart Chen Yunlin, president of the mainland-based Association for Relations Across the Taiwan Straits(ARATS) since June 2008.

    After he served as the SEF chairman, the Chinese mainland and Taiwan signed agreements on weekend charter flights, tourism, direct shipping, air transport, postal services and food safety.

    In the latest round of talks between the SEF and the ARATS heldin Nanjing of eastern Jiangsu Province in late April, the two sides signed agreements on opening regular flights, boosting cooperation in finance and cracking down on crime.

    Wu Po-hsiung, Taiwan's ruling Kuomintang (KMT) chairman, also voiced his support for Chiang.

    Chiang, however, was very insistent on his resignation, according to a Taiwan media report.