Police open fire
A Reuters reporter saw the body of a man in civilian clothes being carried, wrapped in a blanket, into a mosque after police opened fire on the demonstration.
"He had done nothing. He was just looking at the protest then the police arrived and an officer shot at him. He was hit twice in the chest and abdomen," Sherif N'Diaye, a Bairro Militar resident, said as more gunfire rang out.
Officers armed with rocket launchers fired tear gas to disperse the crowd after a tense stand-off.
Army reinforcements later arrived to help patrol deserted streets.
The West African country has been rocked by a series of coups and uprisings since independence from Portugal in 1974 which have kept it one of the poorest nations in the world.
The public buildings in its crumbling capital are decaying and dirt-streaked shadows of their former colonial splendour and many of the city's roads are rutted and mud-choked.
Its security forces are crippled by a lack of equipment. The air force has no planes, the navy is short of functioning ships and the police lack vehicles, radios and computers.
Most senior officers, including the current armed forces chief of staff General Batista Tagme Na Wai, have been implicated in one or more of the military uprisings and plots which have scarred the post-independence years.
Naval chief killed
Lamine Sanha was briefly detained last August, accused of plotting to kill Na Wai and launch a coup.
He was also close to late army leader Ansumane Mane, who overthrew current President Joao Bernardo Vieira after a 1998-99 civil war. Vieira, who first seized power in a 1980 coup, won back the presidency in elections in 2005.
Lamine Sanha died from his wounds on Saturday after being shot several times in the chest, leg and head when he was attacked two days ago by armed men reportedly wearing civilian clothes.
"We want revenge. Lamine Sanha was cruelly assassinated and we want revenge for his death," one of the protesters, Omar Mane, told Reuters in Bairro Militar, a suburb some 4 km (2.5 miles) from the centre of Bissau.