Oluyemi Adeniji raised the issue of seized weapons during a meeting over the weekend with Revolutionary United Front (RUF) leader, Foday Sankoh.
Mr. Adeniji said such practices were in contravention of last year's Lomé Agreement and stressed the "urgent necessity" of returning the weapons seized from Guinean and Kenyan UN troops, the spokeswoman said.
Meanwhile, the latest progress report from the UN mission in Sierra Leone shows that more than 9,000 former rebels have disarmed and registered for the demobilization programme.
Nearly 3,800 of these were from the RUF; some 2,000 from the Armed Forces Revolutionary Council and ex-Sierra Leone Army; and just over 3,400 from the Civil Defence Forces and others. There were more than 730 child soldiers among the newly disarmed.