The three believe the Security Council's membership should be increased from 15 to 25, with six new permanent members and four new non-permanent seats.
The proposal is similar to one presented last year by Brazil, Germany, India and Japan that failed to secure the necessary two-thirds majority in the UN General Assembly.
The proposal ran into opposition from the United States and China, both of whom have permanent seats in the current 15-member UN Security Council.
Brazilian Foreign Minister Celso Amorim said Japan was not formally sponsoring this latest reform proposal.
On 13 December, philanthropist GEORGE SOROS addressed a special plenary session of the UN General Assembly devoted to the implementation of the UN's Millennium Plan for Tajikstan and described the work that his foundation is doing in that country.