The island's security lies not in building up an arsenal of missiles and submarines but in offering assurances that Taiwan is not planning to declare independence, Vice Minister of the Taiwan Affairs Office Wang Zaixi told the newspaper.

Across the Taiwan Strait, the independence-leaning Chen for the first time commented on a proposed "reunification law" the mainland government is considering that could provide the legal basis for attack, saying he was very concerned.

The volleys were the latest in the war of words between China and the democratic island it claims as a breakaway province to be recovered by force if necessary. Tensions have simmered since Chen's election in March to a second four-year term.

Beijing sees Chen's goal of adopting a new constitution by the end of his term in 2008 as a drive toward a formal declaration of independence, and has been preparing for a possible military showdown.

"New tensions and even a serious crisis in the cross-Straits situation may arise if Chen obstinately pursues his timetable," Wang told the China Daily.

The Taiwan leader took part in a rare submarine dive on Thursday to boost military morale days after arch-rival China completed a mock invasion of the island and to assure Washington of Taiwan's commitment to buying US weaponry.

The drill, following China's war games off the island, was intended to boost public support for a huge arms purchase deal with the United States that includes eight diesel-engine submarines, analysts said.

Tension between China and the United States over Taiwan has been rising recently.