The gendarmes were heading to a village in the Toéni region on Thursday after a school was attacked and textbooks torched by armed assailants, a security source told AFP.
According to Reuters, the attack was claimed by Jama’at Nasr al-Islam wa al-Muslimin (JNIM), an umbrella group for al Qaeda-linked militants in the Sahara.
Communications Minister Remy Fulgance Dandjinou said the state of emergency applies to a number of provinces that lie within seven of the country's 13 administrative regions.
The regions are Hauts-Bassins, Boucle du Mouhoun, Cascades, North, Sahel, East and Centre-East.
Names of the provinces where the state of emergency is to be applied will be made public in a presidential decree, he said.
A state of emergency gives additional powers to the security forces to carry out searches of homes and to restrict freedom of movement.
The Sahel state has been battling a wave of jihadist attacks over the last three years, spreading from the north of the country to the east, near the border with Togo and Benin.
JNIM has claimed responsibility for other attacks this year, including one in the capital Ouagadougou in March that killed eight security agents and wounded dozens of others.
Burkina Faso is one of the members of the G5 Sahel, a regional force consisting of troops from Niger, Mali, Chad and Mauritania which has been set up to fight jihadists with the help of countries like France.