TEHRAN, Young Journalists Club (YJC) - Police and soldiers opened fire as the refugees protested over the plan in the town of Kamanyola in eastern Democratic Republic of Congo on Friday, the activists told Reuters.
Congo's government spokesman Lambert Mende denied that those killed were refugees, saying that the clashes broke out when assailants from an unidentified armed group attacked an office belonging to the national intelligence agency.
Five soldiers and 20 of the attackers were killed in the fighting, Mende said.
More than 400,000 refugees have fled Burundi - including 40,000 to neighboring Congo - since violence erupted in April 2015 when President Pierre Nkurunziza said he would seek a third term in office, a move his opponents said was unconstitutional.
Wendo Joel, an activist from a Congolese pro-democracy and human right group, said the refugees had seized a weapon and killed a soldier as they tried to free some of their arrested compatriots.
"The soldiers first fired in the air but there were many refugees," Joel told Reuters. "I have counted 32 bodies. There are also about 100 wounded."
Reuters TV footage showed more than 30 bodies covered by sheets on the roadside in Kamanyola, with many more wounded also lying in the street.
A UN spokeswoman confirmed that at least 18 Burundian asylum seekers had been killed but said the toll was likely to rise. Many others had taken shelter at the UN peacekeeping mission's nearby base, she added.
According to a spokesman for the UN refugee agency, more than 2,000 Burundian refugees live in Kamanyola with host families.
In a statement, Burundi's main opposition grouping, CNARED, accused Burundian army troops and members of the ruling CNDD-FDD's youth group Imbonerakure of carrying out the killings with the Congolese army.
Burundian officials could not be immediately reached for comment, but Burundi's foreign minister Alain Aime Nyamitwe wrote on Twitter: "My heart sinks as I learn of the shootings in Eastern #DRC."
"Clarifications are needed on the shootings and circumstances around," he added.
The violence in Burundi has killed over 700 people and a UN commission said last week there were reasonable grounds to believe authorities had committed crimes against humanity. The government rejected the commission's findings as "propaganda".