Updated

United Nations Secretary-General Ban Ki-moon is calling on politicians in the Congo to place the interests of their country ahead of their own, amid reports of rising political tension in the African nation.

In a statement issued Wednesday, Ban said he was profoundly concerned by the reports and called on "all parties to exercise restraint and express their views peacefully, including in the context of demonstrations scheduled to take place on 26 May."

Tension is building in Congo as President Joseph Kabila maneuvers to remain in office beyond his constitutionally permitted term, U.S. officials and opposition members say.

Congo's top opposition candidate for president flew to South Africa for medical treatment Friday after authorities issued a warrant for his arrest.