The Liberal Democratic Party and its coalition partner Liberal Party agreed Tuesday to begin talks next week with New Komeito on widening the ruling bloc.
The coalition partners also agreed to negotiate among themselves a previous agreement to cut the number of Lower House seats. These discussions will also get under way next week.
The agreement concerning the coalition talks was reached at a meeting of LDP and Liberal Party policy affairs chiefs.
The LDP has begun talks with New Komeito to form the tripartite coalition but it had been uncertain as to when the Liberal Party would join the negotiations.
Several party officials had indicated that the coalition talks would not start until after the LDP presidential election on Sept. 21.
With the results of the LDP-New Komeito negotiations, expected to finish Thursday, the three parties will start "preparation talks" next week before they begin substantial negotiations over the future makeup of the coalition, said Yukihiko Ikeda, LDP policy affairs chief.
The agreement to further discuss the prior LDP-Liberal Party deal to cut 50 Lower House seats allocated through proportional representation was made by the two parties' secretaries general.
A Liberal Party source, speaking on condition of anonymity, said that reaching a three-party agreement on the matter is a precondition to launching a tripartite coalition.
New Komeito, however, firmly opposes the LDP-Liberal Party agreement and hopes to separate the matter from policy talks on forming a tripartite coalition.
During the upcoming policy negotiations, the Liberal Party plans to introduce draft bills that would establish procedures to revise the Constitution, said Hirohisa Fujii, the party's secretary general.