Japanese Prime Minister Kishida Fumio says he takes the result of Tokyo's metropolitan assembly by-elections seriously, in which his Liberal Democratic Party failed to maintain its pre-election strength.

The LDP fielded candidates for eight of the nine seats up for grabs in Sunday's elections. The party won only two, falling short of the five it held before the vote.

Kishida said on Monday that the ruling party needs to learn lessons from the result.

The by-elections were held the same day as the Tokyo gubernatorial election. Incumbent Koike Yuriko won a third term. The LDP backed her.

Kishida said voters gave a positive assessment of what Koike has done by working with the government.

Asked about the forthcoming LDP leadership election, he said he has to give his all to political reforms as well as economic and diplomatic agendas that cannot be put off.

Kishida said he is focused on producing results for them, and he is not thinking about anything else.