The assault on a hotel in the capital, Ouagadougou, was claimed by al-Qaeda in the Islamic Maghreb (AQIM).
The death toll has risen to 30 after a French-Moroccan photographer died from her injuries.
Three gunmen were killed in Friday's operation, Mr Valls said. AQIM on Monday released their photos and names.
AQIM said the assault was carried out by the al-Murabitoun battalion led by Algerian jihadi Mokhtar Belmokhtar.
Six gunmen opened fire on unarmed patrons at the Cappucino cafe before taking refuge at the nearby Splendid Hotel where they held several hostages, the French PM told parliament.
Both places were popular with UN workers and foreign residents.
"Three were killed and three others were being sought," Mr Valls said.
Among the 30 killed were three French nationals, he added.
French special forces based in West Africa were involved in the operation to end the hotel siege in its former colony.
The others who are known to have died include:
Three people involved in last week's Islamist attack in Burkina Faso are still at large, French Prime Minister Manuel Valls has said.