The attack followed parliamentary elections held a week ago in the West African state which donors were hoping would restore stability to an impoverished country that has suffered a string of coups and uprisings since independence from Portugal in 1974.

Foreign donors say the small cashew nut-exporting nation urgently needs political stability to be able to resist the threat of powerful Latin American cocaine cartels which have been using its territory to smuggle tonnes of drugs to Europe.

Guinea-Bissau's national electoral commission announced on Friday that the former ruling PAIGC party, with whom Vieira has had a troubled relationship, had won a clear parliamentary majority in polls held on Nov. 16. But one opposition party leader with links to the military had rejected the results.

"The situation is very serious," Omoregie said, adding an enquiry was underway into who was behind the attack.

Witnesses said the front of Vieira's home in the Tchon de Pepel district of the