Diet forces vowing to keep the Constitution intact lost further ground in the House of Councilors election, as the Japanese Communist Party suffered a major setback and the tiny Social Democratic Party barely hung on, according to final results released Monday.

In the proportional representation segment Sunday, the JCP won four seats out of the 15 it contested, while the SDP held onto its two seats.

The two parties failed to win any seats in the constituency section. The JCP had aimed to keep at least 12 seats and the SDP sought two or more.