TOKYO -- Japanese Prime Minister Yoshihide Suga will resign as early as this month, throwing wide-open the ruling Democratic Party of Japan's presidential election, a crucial race as it could set the tone for upcoming lower house elections.

Also, the LDP's selection process for senior leadership positions has stalled. Suga had wanted to fill the posts by this coming Monday. The likelihood that he would be unable to do so made it difficult for the prime minister to continue running the administration.

Suga had been planning to reshuffle party executives such as secretary-general Toshihiro Nikai, and go into the party's presidential election and the lower house election with fresh faces.

But with the Suga cabinet's slumping approval rating, there was widespread concern from within the party that it will lose the upcoming Lower House race if there is no change at prime minister.

Suga took over after Shinzo Abe resigned last September, citing ill health.