This means that Ishiba no longer has easy control over the upper or lower houses of parliament; last October, the LDP lost control of the more powerful lower chamber, marking a major upset for a party that has ruled Japan for most of its post-World War II history.

The embattled prime minister said he would remain in office to oversee tariff talks with the United States and other pressing matters.

Japanese Prime Minister Shigeru Ishiba said Monday he will stay in office to tackle challenges such as rising prices and high U.S. tariffs after a weekend election defeat left his coalition with a minority in both parliamentary chambers and triggered calls for his resignation.