(Adds background, changes dateline)

YANGON, Oct 12 (Reuters) - Myanmar Prime Minister Soe Win, presumed to have been the architect of an attack on supporters of pro-democracy leader Aung San Suu Kyi in 2003, died on Friday in a military hospital in Yangon, state media announced.

Soe Win, 58, was believed to be suffering from leukaemia and had been treated for several months in a top Singapore hospital.

He returned to the former Burma on Oct. 1 after the failure of a bone marrow transplant, a Yangon-based source said.

His death came after Myanmar's ruling military crushed pro-democracy demonstrations. But it will have little impact on the ruling junta as he had already been replaced as de facto prime minister by Lieutenant-General Thein Sein.

He rose in prominence in 1988 for helping to stifle a nationwide democracy uprising. His replacement of Khin Nyunt after the latter was sacked as prime minister in 2004 dashed faint prospects for political reform.

The United States said Soe Win was believed to have been directly involved in an attack a year earlier on Suu Kyi and her convoy near the central city of Mandalay in a region under Soe Win's control.

Exiled dissidents say dozens were killed by youths wielding bamboo and iron rods. The junta says four people died.

Nobel peace laureate Suu Kyi was imprisoned after the incident and remains under house arrest.

Her National League for Democracy (NLD) won a massive election landslide in 1990 but was denied power by the military.

Myanmar has been under army rule of one form or another since 1962.

AlertNet news is provided by