Japan said on Thursday it will seek information about the arrest of Malaysian opposition leader Anwar Ibrahim during an ASEAN meeting next week.
Japanese Foreign Minister Masahiko Komura is due to head next week to Singapore for meetings with his colleagues from the Association of Southeast Asian nations.
"Japan hopes to use the occasion to grasp the situation so as to decide how to react on the matter," chief government spokesman Nobutaka Machimura told reporters.
Anwar was freed on bail on Thursday after being arrested on new accusations of sodomy, which he dismissed as a conspiracy to thwart his plans to topple the government.
The US said on Wednesday that Anwar's arrest raised "serious concerns".
Japan considers Southeast Asia a key area of influence and entered a free-trade agreement with Malaysia in July last year.