"Subversive elements with negative attitude are resorting to diverse means and ways such as driving a wedge among the national races, misleading the people, and aiding and abetting anti-government groups to weaken and break up the Union," Senior General Than Shwe said in a national "Union Day" address.

The former Burma's official name is the "Union of Myanmar".

The 75-year-old military supremo's message was carried in all official newspapers and on a televised ceremony from the new capital, Naypyidaw, although a power blackout in the old capital, Yangon, ensured few people there got to see it.

His exhortation to the southeast Asian nation's 53 million people to "make endeavours for the emergence of an enduring State Constitution" comes three days after the announcement of a referendum on the army-drafted charter in May.

The opposition National League for Democracy (NLD), which won a 1990 election landslide only to be denied power by the military, was excluded from the constitution-drafting process and is expected to push for a "no" vote.

The NLD is expected to make its position clear later on Tuesday even though party chief Aung San Suu Kyi remains incommunicado under house arrest -- as she has been for most of the last 18 years.

The "88 Generation Students", a group of leading dissidents from a failed 1988 uprising, have already dismissed the charter as an attempt by the generals to legitimise their iron grip on power, and have urged people not to endorse it.

It was also rejected by the underground All Burma Monks Alliance, which played a role in last September's pro-democracy protests which evolved from small demonstrations against shock fuel price rises and were crushed by the regime.

The group vowed to "keep on fighting by all means in order to help the entire people get over poverty and destitution".

The United States says the referendum will be a sham conducted in a "pervasive climate of fear". The United Nations, which is trying to foster talks between the generals and Suu Kyi, has been more cautious in its criticism.

The February 12 "Union Day" dates back to a 1947 agreement between the Burmese majority and minority groups to demand independence from Britain.

The country has been under military rule since 1962 and has been riven by dozens of guerrilla conflicts with ethnic militias, mostly in the mountainous border areas abutting Thailand, China, Bangladesh and India.

More than 1,100 people are imprisoned on account of their political or religious beliefs, the United Nations says, and hundreds more have fled persecution to neighbouring countries.