The UN mission in the Democratic Republic of Congo, Monuc, says it has confiscated weapons from former rebel military commanders.
The UN has reinforced its contingent in Bukavu
UN spokesman Sebastien Lapierre said the weapons were found in houses of several colonels of the rebel RCD-Goma.
He told the BBC the discovery was made in the strategically important town of Bukavu, on the border with Rwanda.
The former rebels - who are now part of the government - say the weapons belonged to their bodyguards.
Last month similar finds were made in the house of the town's governor.
A UN official has said the Congolese military should take appropriate measures to control the flow of weapons in the town.
A BBC correspondent in DR Congo says this will not be easy, due to serious divisions in the local army command.
Despite the peace process and the setting up of a government of national unity last year, the situation is still tense in the far east of the country.
A 3,500-strong brigade of UN peacekeeping troops has been deployed in Bukavu after reports of incidents between former rebels and supporters of the President Joseph Kabila in the town.