Anti-government gunmen simultaneously attacked two military sites in the Burundi's capital of Bujumbura, aiming to seize weapons and free people held in prison early on Friday.
12 insurgents have been killed and 20 people arrested, the army said later in the day.
Five soldiers were also wounded, army spokesman Gaspard Baratuza told the state radio.
The clashes started around 4am local time (06:00 GMT) when “heavily armed men” attacked an army base in Ngagara in the north of the city and the ISCAM Higher Institute of Military Training in Musaga in the south, a senior military official who asked not to be named told AFP.
The clashes lasted several hours, but later in the morning Willy Nyamitwe, the presidential media adviser, said the situation is returning to normal.
— Willy Nyamitwe (@willynyamitwe) December 11, 2015
The country has been rocked with a cycle of violence since President Pierre Nkurunziza announced his bid for third term in April, despite a two term limit in the constitution. Despite the unrest and clashes, the elections were held in summer and Nkurunziza won a third term.
The opponents, who are referred as "Sindumuja," meaning "I am not a slave", say it contradicts the deal that ended the civil war in 2005.
Burundi suffered from a civil war between 1993 to 2005 and some 300,000 people died in the conflict between rebels from the country's majority Hutu population and an army dominated by the Tutsi minority.
At least 250 people have died in the latest violence and more than 210,000 people have fled to neighbouring countries.
The United Nations has warned on Tuesday that there is risk of civil war in Burundi if deadly violence is not stopped.