More than 3,000 people have died in the region since 2016, with some 1.4 million displaced.
Fighting Tuesday in the DR Congo's southern opposition stronghold of Kasai killed three men thought to belong to the anti-government Kamwina Nsapu militia, military and local sources said.
Witnesses reported hearing light and heavy weapons fire near the region's main Kananga airport early Tuesday morning.
Around 30 youths wearing red headbands had staged an impromptu rally near the airport shouting slogans associated with Kamwina Nsapu, an airport source said.
"The army responded with heavy weapons fire and three youths fell," a military source who requested anonymity told AFP, confirming that they belonged to the militia group spawned by the death of tribal chieftain Kamwina Nsapu in August 2016.
He was the figurehead of a rebellion against the central government in Kinshasa over moves by President Joseph Kabila to prolong his power.
More than 3,000 people have died in the region since then, with some 1.4 million displaced.
Kananga's mayor, Edouard Ntumba Buabua, confirmed the Kananga clash, which came after protesters in the faraway capital Kinshasa, led by Catholic and opposition groups, on Sunday defied a ban on demonstrations demanding that Kabila leave office.
State forces fired tear gas into churches and bullets in the air to break up the gatherings, with as many as 11 feared dead, according to organisers.
DR Congo is one of the UN's global humanitarian priorities for 2018, with four million internally displaced people and hundreds of thousands of children at risk in Kasai, according to warnings from aid agencies.
Two UN experts were killed in March while investigating violence in the region, where the United Nations has counted more than 80 mass graves.