But a United Nations official cast doubt on the claim and said the U.N. was confident the country would remain calm for the country's long-delayed vote, now set for July 30.
The suspects arrested Tuesday were former soldiers who worked for a Congolese security company, Interior Minister Theophile Mbemba said. He said the men were arrested with military gear, but did not provide further details about the type of weapons they had.
They "were working in Kinshasa as security guards but it is clear that they were military personnel with political plans," Mbemba said. "They were part of a coup attempt, and they will face justice in Congo."
He said there were three Americans, 10 Nigerians and 12 South Africans among the group of 32 taken into custody. Mbemba said all the men had received visits from their respective ambassadors.
South Africa's ambassador said 19 of those arrested had South African papers. It was not immediately possible to resolve the discrepancy between that number and Mbemba's figure. Ambassador Sisa Ngamane said the country had sent identification documents to the authorities for the arrested South Africans and that it expected to be kept apprised of the investigation.
A South African government statement said 16 of the South Africans worked for the Omega Security Company, while the remaining three worked as interpreters for a mining firm.
U.S. Embassy official Katya Thomas declined to comment, saying officials were still working to confirm the three were American citizens. She said she could not release any more information.
Nigerian Embassy officials in Congo were not immediately available for comment.
The United Nations said it could not confirm Congo's allegations.
"We are not concerned about this, it appears to be a case of political manipulation by Congo's government," said Jean-Tobias Okala, a U.N. spokesman in Kinshasa. "We have almost 18,000 troops here to achieve our goal of peaceful and transparent elections."
Separately Wednesday, hundreds of demonstrators marched in Kinshasa to protest the delay of the election — originally to be held by June 30. They also objected to the government's refusal to reopen voter registration so that opposition supporters who had planned to boycott the vote could register.