By John Geddie and Tim Kelly TOKYO (Reuters) -Japanese Premier Shigeru Ishiba vowed to remain in his post on Monday after his ruling coalition suffered a bruising defeat in upper house elections, prompting some in his own party to doubt his leadership as the opposition weighed a no-confidence motion.

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.