An opposition lawmaker was expelled from his party Tuesday amid growing criticism over his remarks on the possibility of Japan waging war with Russia to regain control of a group of islands at the center of a territorial spat.

House of Representatives member Hodaka Maruyama on Tuesday submitted a letter of resignation to Nippon Ishin no Kai after he asked the head of a group of former residents of the islands whether he would support a war with Russia. Later in the day, the party decided to expel Maruyama rather than accept his resignation.

"His acts and remarks were inexcusable as a national lawmaker. This is also a serious issue in terms of diplomacy. I think he should resign as a lawmaker," said Osaka Mayor Ichiro Matsui, who also heads Nippon Ishin.