LUBUMBASHI, DEMOCRATIC REPUBLIC OF CONGO - The U.N. peacekeeping mission in Congo on Monday condemned the arrest of about 30 opposition members amid a crackdown on dissent by President Joseph Kabila's government.

The arrests occurred in the eastern city of Lubumbashi on Sunday when police broke up a meeting by the Union for Democracy and Social Progress (UDPS) party on the eve of a return to the city of opposition leader Felix Tshisekedi after a long absence, party members told Reuters.

Congo is struggling to deal with high political tension and security concerns are threatening to spiral out of control in Africa's largest copper producer because of Kabila's refusal to hold elections when his presidential mandate expired nearly a year ago.

The election commission said earlier this month that an election to replace Kabila, who came to power after his father's assassination in 2001, will not be possible before April 2019 at the earliest — raising the prospect of long-term unrest.

"I urge the Congolese authorities to release immediately and unconditionally those arbitrarily arrested yesterday in Lubumbashi," said Maman Sidikou, head of the U.N.'s MONUSCO peacekeeping mission.

MONUSCO also demanded an end to restrictions imposed on Kyungu wa Kumwanza, president of the National Union of Federalists of the Congo (UNAFEC) party, who has been under de facto house arrest for several months without being charged with a crime.

Congo's government has banned opposition demonstrations since last year, when security forces killed dozens of protesters demanding Kabila's departure.

Kabila's political opponents are weak and divided. Many joined a power-sharing government earlier this year following the death of opposition icon, Tshisekedi's father Etienne, and they enjoy limited credibility with the population.

However, an economic crisis that has seen inflation spike to over 50 percent, increased militia activity, and a series of prison breaks have highlighted Kabila's tenuous hold on power.