Police said that on Sunday they arrested 28 supporters of the main opposition Union for Democracy and Social Progress (UDPS)
The UN's envoy for DR Congo on Monday called on the Congolese authorities to release a group of opposition members arrested Sunday for allegedly insulting President Joseph Kabila.
"I call on the Congolese authorities to release immediately and unconditionally those people who were arbitrarily arrested yesterday in Lubumbashi," Maman Sidikou, the UN's special representative and mission head for Democratic Republic of Congo, said in a statement.
Sidikou also reminded the authorities of their duty to guarantee citizens' rights "in line with the constitution and DR Congo's international commitments."
Police said that on Sunday they arrested 28 supporters of the main opposition Union for Democracy and Social Progress (UDPS).
Party sources said 48 were detained in Lubumbashi in the country's restless southeast.
In a statement, the UN mission MONUSCO condemned the arrests and said it was "extremely concerned by continued acts of intimidation of members of the opposition."
They were detained during a private meeting at party headquarters, it said
"A total of 28 (party activists) were detained and jailed. They will be judged under the law," regional police commandant Paulin Kyungu told AFP on Sunday, saying the group had insulted Kabila.
Tensions are running high in the country after Kabila failed to step down after his second and final term expired last December.
Elections were supposed to have taken place this year under a transitional deal aimed at avoiding fresh political bloodshed in a country beset by ethnic divisions and bloody fighting in its east.
But the country's electoral commission earlier this month announced there will be no vote before early 2019 in the vast country, sparking fresh security worries.
The international community has strongly urged a clear poll timetable be released, with the United Nations the current situation has created "tensions and a climate of uncertainty".
UDPS leader Felix Tshisekedi, who was scheduled to arrive in Lubumbashi on Monday, earlier this month accused Kabila and the electoral commission of having "declared war on the Congolese people" by delaying the poll.