TOKYO (Reuters) - Japanese Prime Minister Shinzo Abe’s ruling bloc suffered two rare losses in by-elections on Sunday in an apparent warning from voters not to get complacent ahead of a national election for parliament’s upper house later this year.

FILE PHOTO: Japan's Prime Minister Shinzo Abe delivers a press conference standing next to the calligraphy 'Reiwa' which was chosen as the new era name at the prime minister's office in Tokyo, Japan, April 1, 2019. Franck Robichon/Pool via Reuters

The defeats in a lower house by-election in Osaka, western Japan, and another on the southern island of Okinawa - host to the bulk of U.S. military in the country - were the first such losses since Abe returned to office in December 2012, except for one uncontested poll.

“Each individual (ruling) Liberal Democratic Party member must take the results to heart and buckle down,” Abe told reporters on Monday morning.

The defeats in the Sunday polls come after Japan’s Olympics minister, Yoshitaka Sakurada, resigned a year before the Tokyo Games for remarks that offended people affected by the massive earthquake and tsunami that triggered nuclear meltdowns in 2011. A vice transport minister also quit over a separate gaffe.

“The cabinet support rate is maintaining a certain level, but if they do not eradicate laxity and conceit, the upper house election will perforce be a difficult fight,” said an editorial in the conservative Yomiuri newspaper.

Support for Abe’s cabinet was at 47 percent in a survey by public broadcaster NHK released this month, up five points from the previous month.

In Okinawa, Tomohiro Yara, a free-lance journalist backed by several opposition parties and running on an anti-U.S. base platform, defeated a former cabinet minister.

In Osaka, Shimpei Kitagawa, backed by the LDP and its junior partner Komeito, lost to Fumitake Fujita from Nippon Ishin) (Japan Innovation Party), a conservative Osaka-based party that sometimes cooperates with the LDP nationally.

Speculation is simmering that Abe will call a snap lower house election in tandem with the upper house poll, possibly after announcing the postponement of a sales tax hike to 10 percent from eight percent scheduled for October.

Top government officials vowed on Friday to go ahead with the tax rise, barring a big economic shock.

Such a “double election” might help take advantage of weakness among the fragmented opposition parties, but could also spark the opposition to cooperate on candidates.

“Abe must be wondering which suffers more from weakness - LDP/Komeito or the opposition,” said Sophia University political science professor Koichi Nakano.

“A double election will also potentially galvanize the opposition into action ... so it’s a double edged sword,”