The incident was the latest in a series of attacks, raising fears of a fresh rebellion against the government in the central African nation. Five gunmen, two soldiers, a policeman and a civilian were killed in the latest clash.
"Police and army are leading a joint operation against groups of gunmen who on Tuesday ambushed two transport vehicles," army spokesman Colonel Gaspard Baratuza told Reuters.
Baratuza said the attack occurred in Burundi's western province of Cibitoke bordering the Democratic Republic of Congo. He declined to say whether the assailants were rebels or bandits.
On Monday night, three people were killed in different attacks by gunmen in the south and east of the landlocked coffee producing country.
The attackers also set fire to a pineapple farm belonging to President Pierre Nkurunziza, local media reported.
Burundi has enjoyed relative peace since the former rebel Forces for National Liberation(FNL) laid down weapons and joined the government in 2009, after two decades of civil war.
But more people are now voicing dissent and demanding President Nkurunziza start talks with opposition leaders in exile who fled the country after 2010 elections.
Among those in exile is former rebel leader and FNL boss Agathon Rwasa. Rwasa is in hiding, saying he fled to avoid arrest by Burundi's government which has accused him of planning a new insurgency.
Rwasa was a presidential candidate in Burundi's 2010 elections but later withdrew from the race, accusing the ruling CNDD-FDD party of rigging the votes.