TOKYO (Kyodo) -- Prime Minister Shigeru Ishiba said Sunday that his Liberal Democratic Party and its coalition partner must at least retain majority control of the upper house in the summer election after a setback in last year's polls for the more powerful lower house forced the formation of a minority government.

"We should retain a majority of (seats in) the upper house as a ruling coalition. This is our baseline," Ishiba said on a TV program ahead of the beginning of a 150-day regular session of Japan's parliament on Friday.

The election must be held by late July, with half of the 248-member House of Councillors seats up for grabs. Upper house members serve six years in Japan, and an election in which half of the chamber's seats are contested takes place every three years.

Ishiba did not rule out dissolving the House of Representatives for a snap election if a no-confidence motion against the Cabinet is approved.

The regular Diet session will be Ishiba's first since the LDP and Komeito lost their majority in the lower house following the Oct. 27 election. After taking office on Oct. 1, Ishiba swiftly called a general election to strengthen his hold on power, but the strategy backfired.

Uncertainty looms over whether Ishiba's minority government can pass the state budget for the next fiscal year, as opposition parties are expected to maintain a confrontational stance over a fundraising scandal involving LDP lawmakers.

Yoshihiko Noda, head of the main opposition Constitutional Democratic Party of Japan, said opposition parties will aim to block the ruling parties from securing a majority in the upper house election.