Japanese officials met with the leader of a major Syrian rebel group in Turkey on Monday night to seek its assistance in securing the release of a Japanese man believed to have been captured in northern Syria by the Islamic State militant group.

The meeting with Syrian National Coalition chief Hadi al-Bahra took place in Istanbul at the request of the Japanese government, a rebel group source said on Wednesday. But the Japanese Foreign Ministry's task force in Jordan declined to confirm the contact.

The meeting is the first known concrete action by the Japanese government in its efforts to ascertain whether 42-year-old Haruna Yukawa has indeed been captured and, if so, what kind of situation he is in.

While details of the meeting remain unclear, the source said in the talks with the coalition president, the Japanese side requested assistance in securing the man's release.

Yukawa is believed to have been traveling with rebel fighters from the Islamic Front and the Free Syrian Army when he was captured by the Islamic State during a firefight in Marea, roughly 30 kilometers north of Aleppo, on Thursday.

The Western-backed Syrian National Coalition, which is seeking to topple the government of President Bashar Assad, is aligned with the Free Syrian Army. But its direct impact on battlefields is limited, leaving it unclear whether Tokyo's request to Syria's main opposition alliance would yield any results.

Islamic Front and Free Syrian Army leaders say they offered to trade captured Islamic State fighters for Yukawa but had received no reply as of Tuesday.