TOKYO, May 14 (Xinhua) -- The Japan Innovation Party on Tuesday expelled lower house lawmaker Hodaka Maruyama over remarks he made insinuating Japan using war to regain control over islands central to a territorial spat with Russia.

The head of the opposition party, Osaka Mayor Ichiro Matsui, said Matsui should be removed from the party as his remarks were intolerable.

"It's outrageous for a Diet member to have made such remarks and it's also an extremely grave issue from a diplomatic standpoint. He should now step down as a lawmaker," Matsui told a press briefing on the matter.

Maruyama, 35, made the remarks on Saturday as he joined a group of former residents of Kunashiri Island off Hokkaido from Friday through Monday under a Japan-Russia visa-free exchange program.

According to the head of the group of former residents, Maruyama asked him while drunk, "Do you think there is any alternative to war to recover the islands?"

The head of the group dismissed the remark, and Maruyama officially retracted the comments on Monday amid stern condemnation from Russia.

Following a Japan Innovation Party committee meeting convened on Tuesday at its headquarters in Osaka, the committee unanimously decided to expel Maruyama.

The committee said Maruyama's remarks had led to public mistrust.

Japan's top government spokesperson, Chief Cabinet Secretary Yoshihide Suga, slammed Maruyama's remarks as being "extremely regrettable," adding that Tokyo remained committed to resolving the territorial dispute with Moscow through diplomatic means.

The islands at the center of the dispute between Tokyo and Moscow are known as the Northern Territories in Japan and the Southern Kurils in Russia.

The decades-old territorial spat has prevented the two countries from signing a post-World War II peace treaty and hindered diplomatic and trade relations between the two countries.

Both parties have, however, provisionally agreed to discuss furthering joint economic activities on the islands and Japanese Prime Minister Shinzo Abe has made it one of his priorities as leader to continue to strive to resolve the territorial issue and sign a peace treaty.