Chen, under pressure to resign over corruption scandals, raised the issue of a new "constitution" at a seminar on Sunday sponsored by his independence-leaning Democratic Progressive Party (DPP).

The Taiwan leader raised the possibility of changing the territorial definitions of Taiwan.

Reacting to the move, the US State Department said on Monday that Washington "does not support independence for Taiwan, and we continue to be opposed to unilateral changes in the status quo by either side."

The United States took "very seriously" Chen's "repeated commitments not to permit the 'constitutional' reform process to touch on sovereignty issues, which includes territorial definition," State Department deputy spokesman Tom Casey told reporters. "We expect him to carry out those commitments, and we'll see what happens."

The fulfilment of the commitments, Casey said: "is a test of his leadership, as well as his ability to protect Taiwan's interests, its relations with others, and to maintain peace and stability in the Straits."

The National People's Congress last year approved the Anti-Secession Law to deter any secessionist scheme to seek formal "independence" for the island.

Taiwan is an inalienable part of China, and both the mainland and Taiwan belong to one and the same China, although the two sides of the Straits are yet to be reunified as a result of the country's civil war in the late 1940s.

Chen told the seminar on Sunday that Taiwan should overhaul its "constitution" which was enacted by the Kuomintang (KMT) government in 1947 and has gone through seven amendments since 1991.

Under the "constitution," Taiwan's territory included all of China, but in reality only Taiwan and some offshore islands were ruled from Taipei, he said. Chen has previously shunned the sensitive topic on territory by saying Taiwan needs a new "constitution" only to enhance government efficiency.

In a related development, Taiwan's opposition People First Party (PFP) yesterday proposed a new recall vote in the "legislature" in a renewed effort to oust Chen.

The first opposition attempt to launch a recall which would include an island-wide referendum on Chen's fate failed in June when fewer than the required two-thirds of "lawmakers" voted in favour.

The proposal came after a call on Monday by KMT Chairman Ma Ying-jeou for a new recall motion.

A "legislative" committee agreed yesterday to consider the PFP motion. Chen's ruling DPP said in a statement it opposed the move.

The fresh attempt to topple Chen comes after hundreds of thousands of people, led by former DPP chairman Shih Ming-teh, took to Taipei's streets this month calling for him to go.

The round-the-clock demonstration in downtown Taipei began on September 9. Smaller rallies in southern Taiwan this week led to scuffles between anti- and pro-Chen camps.

Chen, who was elected in 2000 and re-elected in 2004 by a thin margin, has been questioned over the undocumented use of more than 36 million new Taiwan dollars (US$1.12 million) from his confidential "state" affairs budget of last year.

His wife, Wu Shu-chen, is accused of accepting millions of Taiwan dollars in department store gift certificates, but Chen has rejected the accusation. His son in-law, Chao Chien-ming, is facing insider trading charges and fighting them in court. Chen's ex-deputy chief of staff faces corruption charges.