TOKYO, Jan. 15 (Xinhua) -- Two of Japan's opposition parties on Monday exchanged a document on consensus on their basic policies as they agreed to form an alliance in parliament.

While an official merger has not yet been confirmed, Motohisa Furukawa, secretary general of the Party of Hope and Teruhiko Mashiko, who serves the same position in the Democratic Party, vowed to create an alliance that could challenge the ruling Liberal Democratic Party (LDP).

If the merger comes to fruition, the alliance would create the largest opposition group in both chambers of Japan's parliament, overtaking the Constitutional Democratic Party of Japan (CDPJ).

Launched by Tokyo Governor Yuriko Koike just prior to the Oct. 22 last year lower house election, the Party of Hope absorbed a number of conservatives from the Democratic Party to run on its ticket, while many liberals from the then moribund Democratic Party joined the CDPJ ahead of the election.

The two parties may officially confirm the alliance later this week, with Mashiko quoted as saying a merger could happen if momentum increased within the parties.

If the move were to happen, the number of members of the two parties in the more powerful lower house of parliament would stand at 65, compared to 54 of the CDPJ.