TOKYO

Japan is investigating reports that a journalist is being held captive by an al-Qaeda affiliated group in Syria, after a video of the man was uploaded to Facebook this week.

The group -- the al-Nusra Front -- has been classified by Turkey as a terrorist organization since June 2014, but analysts say other groups fighting Bashar Assad's regime have now become more dominant.

When contacted by Japanese news agency Kyodo on Thursday, a Syrian man who uploaded the footage said that he had received the video of Jumpei Yasuda from a person representing the group.

He said that the group -- which has been fighting Assad since 2011 -- is demanding a ransom from the government, but it is yet to respond.

In December 2015, rights group Reporters Without Borders said in a statement that Yasuda has been held by an armed group in Syria since July.

It added that his captors had threatened to kill him or sell him to another group unless a ransom was paid.

It did not name which group was reportedly holding Yasuda, but said he was kidnapped in an area controlled by the al-Nusra Front soon after entering the war torn country.

On Thursday, Chief Cabinet Secretary Yoshihide Suga told a press conference that the man is likely to be Yasuda, but said the government was not aware of any ransom demand being made.

"We are utilizing various information networks [to deal with the matter]," Kyodo reported him as saying.

He declined to comment on whether the government has directly contacted the group.

In the video, the man -- wearing a black sweater and a scarf -- speaks in English for around one-minute from a white-walled room.

"Hello, I am Jumpei Yasuda and today is my birthday, 16th March," he says.

"I have to say to something to my country. When you're sitting wherever you are, in a dark room, suffering with the pain. There's still no one. No one answering. No one responding. You're invisible."

Bunyamin Keskin, a research assistant at the Foreign Policy Research Department of SETA in Ankara, said that Turkey has classified the al-Nusra Front as a terrorist organization since June 2014, but it is not as dominant as it once was.

"After Russia’s involvement in Syria, Russia made operations not just against opposition groups that Turkey sees as mild, but also against al-Nusra," he said.

"If we see the situation as a balance of power, mild opposition groups have more dominance in the area than al-Nusra right now."

In Sept. 2014, al-Nusra kidnapped 45 Fijian United Nations peacekeepers on the Syrian-Israeli border, claiming they were aiding Assad, but they were released two weeks later.

In Aug. 2014, it released U.S journalist Peter Theo Curtis after holding him for almost two years.

Keskin said al-Nusra has also kidnapped fighters being trained within the scope of Turkey and the United States' Train and Equip program, but they may well have been their own men working undercover.

Last year, fellow terrorist group Daesh killed two Japanese hostages -- freelance journalist Kenji Goto and contractor Haruna Yukawa -- in Syria.

- Anadolu Agency correspondent Satuk Bugra Kutlugun contributed to this story from Ankara