African leaders, holding their annual summit in Ouagadougou, Monday observed a minute of silence in memory of Nigerian military ruler Gen. Sani Abacha, who died of heart attack earlier Monday.

The new chairman of the OAU, Presidemt Blaise Compaore of Burkina Faso, said he received the news of the death with shock.

He then requested his colleagues to observe silence for a solemn one minute as a tribute to Abacha, 54, who backed efforts by the West African Economic Community to restore peace and democracy in Liberia and Sierra Leone.

In his reaction, ECOWAS Executive Secretary Lansana Kouyate told PANA that Abacha's death was particularly ''painful'' because of the role Nigeria has been playing in the sub-region during his tenure of office.

''We pray that Nigeria goes through the transition peacefully,'' Kouyate said, adding that he said he was cutting short his stay in Ouagadougou to return to Nigeria.

Ibrahima Samba, WHO's Regional Director for Africa said ''the sudden death of a leader is painful and there is the uncertainty of the after-event.''

''With one quarter of Africa's population every African should be concerned about the events in Nigeria,'' he said.

News of the death has dampened the mood at the 34th OAU Summit.

Nigerian foreign minister Tom Ikimi, who represented Abacha at the openig ceremony, was reported to have left for home after receiving the news.

An advance party of the Nigerian leader left Oaugadougou early Monday, when the the general failed to show up.

Abacha took power in November 1993 from an interim civilian administration appointed by former military ruler Gen. Ibrahim Babangida, who stepped aside in August after annulling results of presidential elections of June that year, in which his friend, millionnaire politician Moshood Abiola claimed victory.

The effects of the political crisis unleashed by the cancellation of the poll continues to linger in Nigeria, which is under U.S. and European Union sanctions over democracy and huma rights issues.

Until his death, Abacha, who seldom appeared in public, was implementing a transition-to-democracy programme scheduled to end 1 October.

The recent adoption of the general as the sole candidate for the August 1 presidential elections provoked a national controversy, with opposition groups dismissing the programme as a ruse.

It is not clear what would happen to the transition programme with the death of Abacha, who made silence and suspense his greatest asset.