BISSAU—At least six people were killed in a failed attempt to overthrow Guinea-Bissau’s President Umaro Sissoco Embalo, state radio said on Wednesday, as residents of the capital cautiously returned to daily life. The dead in Tuesday’s assault included four assailants and two members of the presidential guard, it said. Embalo had announced on Tuesday night that the situation was under control after gunfire rang out for more than five hours near a government compound where he was holding a cabinet meeting. The West African country, which has a population of about 2 million, has witnessed 10 coups or attempted coups since independence from Portugal in 1974. Only one democratically elected president has completed a full term. West Africa has been hit by a string of military takeovers over the past 18 months—including two in Mali, one in Guinea, and one in Burkina Faso just last week—leading analysts to warn about …