Burundi says it is deploying about 100 soldiers to North Kivu province in eastern Democratic Republic of Congo, where dozens of armed groups are fighting.
They are to join a regional East African force – which also includes soldiers from Kenya.
It was deployed in November following the resurgence of the M23 rebel group which Rwanda is accused of backing but the Kigali government denies.
The rebels are due to withdraw by the end of the month from areas they have captured.
Previous deadlines have been missed and there have been recent demonstrations in eastern Congo by people who want the East African force to take a more aggressive stance against the rebels. BBC