Yangon - Myanmar's main opposition party marked Union Day Thursday by launching a nationwide petition campaign to free its leader, Aung San Suu Kyi, who has been under house arrest since mid-2003.

Hundreds of National League for Democracy (NLD) members and supporters kicked off the "Free Suu Kyi" campaign by signing their names on a signboard at the party's headquarters in Yangon on the holiday that marks the 1947 call for independence by Myanmar's ethnic groups.

"We started the signature campaign today for the freeing of Daw [Madame] Aung San Suu Kyi, U Tin Oo and all political prisoners," NLD spokesman Nyan Win said.

"We plan to hold similar campaigns in other provincial townships because we want to show both the authorities and international community how people support freeing the political prisoners," Nyan Win said.

Nobel Peace Prize laureate Suu Kyi has been under house detention since May 2003, as has her chief deputy Tin Oo. Altogether, Myanmar's junta has jailed more than 2,500 political prisoners with some of them serving 65-year sentences or more for participating in protests.

Nyan Win said the signature campaign broke none of the laws in military-run Myanmar.

In a ceremony marking Myanmar's 62nd anniversary of Union Day, the NLD also called on the government to release all political prisoners, convene parliament and allow the party to reopen its regional branches.

The NLD won the 1990 general election but has been denied power for the past 19 years by the country's military regime. Suu Kyi, the daughter of Independence hero Aung San, has spent about 13 of the past 19 years under house arrest in her family compound in Yangon, once called Rangoon.

Diplomats from the United States, France, Britain, Germany and Italy attended the ceremony, which also drew about 300 NLD supporters.

Although the military has shifted its capital to Naypyitaw, all embassies remain in Yangon.

In Naypyitaw, about 350 kilometres north of Yangon, Union Day was marked with a speech by the military supremo, Senior General Than Shwe.

The junta chief called on "all the national races to make endeavours for building a new, modern, developed, discipline-flourishing, democratic nation in accordance with the state constitution massively approved by the people."

Than Shwe last year pushed through a national referendum on a constitution that basically cements military rule in Myanmar's future.

The drafting of the constitution and the referendum are part of the regime's "seven-step road map" to democracy, which is to include a general election some time next year.

Myanmar, also known as Burma, has been under military rule since 1962. The country enjoyed only a brief spell of democracy after achieving independence from Britain in 1948.

Union Day marks the day when General Aung San met with leaders of ethnic minority groups to sign an agreement at Pinglon Town in Shan State demanding that the British government restore independence to Myanmar. (dpa)