Opposition parties need to work together in this summer's Upper House election to prevent the ruling Liberal Democratic Party from gaining more Diet seats and landing a majority in the chamber, former Democratic Party of Japan leader Ichiro Ozawa said Tuesday.

"We cannot allow the LDP to continue being the sole winner," said Ozawa, now a rank and file member of Seikatsu No To (Lifestyle Party). "The Upper House election in the summer is the showdown."

Looking back on the Dec. 16 Lower House election in which the LDP trounced the DPJ and came away from the poll with a majority, Ozawa said one of the biggest reasons Nippon Mirai no To (Tomorrow Party of Japan), the party that he belonged to for the poll but which split up last week after only a month since its founding, suffered so badly was its failure to join hands with other opposition parties during the short time leading up to the Dec. 16 election.

"I had talks with Toru Hashimoto, deputy leader of Nippon Ishin no Kai (Japan Restoration Party), and Your Party President Yoshimi Watanabe on the possibility of cooperation. But they did not bear fruit and the outcome was as predicted," Ozawa said.

Ozawa made the comment during a New Year's party at his private residence in Tokyo with his close aides. The party is an annual event for them. When Ozawa was still in the DPJ, more than 100 lawmakers came to the party.

However, with Ozawa belonging to a week-old minor party, only about a dozen lawmakers, including Seikatsu no To leader Yuko Mori, and other former lawmakers who lost their Diet seats in last month's election, came.