The Congolese army said the fatalities took place in the eastern province of South Kivu over the past four days, accusing Mai Mai Mazembe militiamen from the Nande ethnic group of being responsible for both attacks.
"The army recorded a loss of nine soldiers in two ambushes in the Baraka operational zone" in South Kivu, an unnamed military official told AFP.
A lieutenant was killed on Sunday in the village of Lweba, seven kilometers from the Baraka district, the official said, adding that the other deaths came in an attack two days earlier.
"Our hospital received the bodies of eight soldiers killed by bullets on Friday," said a hospital source in Lulimba, a village 60 kilometers south of Baraka.
Dozens of armed groups have been active in the eastern DR Congo ever since a war there in 1998, and the Congolese army, joined by United Nations troops, is on the offensive against rebel groups.
Seeking safety, tens of thousands of people have escaped to neighboring Zambia, where they are facing “hugely underfunded” aid operations, according to UN figures.
Congo has also been facing numerous problems over the past few decades such as grinding poverty and crumbling infrastructure.
Political crisis has exacerbated in the African country as President Joseph Kabila is still in power despite his second and final term as president officially ending in December 2016.
Under the DR Congo's constitution, Kabila is banned from seeking a third term. However, Kabila is authorized to stay in office until his successor is elected.
The long-awaited election to replace Kabila has been postponed until December 23, 2018. The delay in holding an election has flared up violence in the country.