Gunmen attacked the army's headquarters in the capital of Burkina Faso on Friday as well as the downtown area and France's embassy, and the French ambassador said an explosion in the city was a terrorist attack.
It was not clear who was behind the violence but Burkina Faso and other West African countries have been targeted by jihadist groups linked to al Qaeda and Islamic State in the past few years.
A local news station showed pictures of black smoke coming from a building in central Ouagadougou and a Reuters correspondent found that most people had fled the streets.
"Attack under way at the French Embassy and French Institute. Stay hidden where you are," the embassy said in a statement posted on its Facebook site.
A French official in Paris confirmed that an assault against the embassy was under way, as well as against the Burkina Faso army headquarters.
An explosion rocked the army headquarters and then gunfire rang out in the vicinity. A witness said masked gunmen with backpacks had attacked the army headquarters shortly before the explosion.
Islamist militants have gained a stronger foothold in Africa's vast Sahel region in the last few years, launching attacks in Mali, Burkina Faso, Ivory Coast and Niger.
Suspected jihadists killed at least 18 people last August during a raid on a restaurant in Ouagadougou, and militants have targeted Burkinabe security forces along its remote northern border region with Mali.
Al Qaeda in the Islamic Maghreb (AQIM) claimed responsibility for an attack on a restaurant and hotel in Ouagadougou in January 2016 in which 30 people were killed.
Five countries launched a new taskforce last year to tackle Islamist militants in the region, to which international donors have committed half a billion dollars.
Jean-Marc Châtaigner, France's ambassador to West Africa's Sahel region, tweeted: "Terrorist attack this morning in Ouagadougou, Burkina Faso: solidarity with colleagues and Burkinabe friends." He urged people to avoid the city centre.
After the first big blast, the sound of a series of smaller explosions and exchanges of gunfire came from the direction of the headquarters. It ceased by around noon.