U.N. Secretary-General Ban Ki-moon says the U.N. Security Council should be "more democratic and representative," but did not directly answer Nigeria's bid to become a permanent member of the council.
Ban spoke during a Monday visit to Nigeria's capital, Abuja.
The West African nation contributes the fourth-largest contingent to peacekeeping missions and has been lobbying for a permanent seat for about a decade.
Nigerian President Goodluck Jonathan says the fact that no African nation holds permanent membership is "unfair and untenable." French President Nicolas Sarkozy has said he supports Nigeria's campaign.
France has occupied one of the five veto-wielding permanent seats since the Council's creation in 1946. Nigeria currently occupies one of the 10 rotating seats.