* Video clip shows man being questioned, giving name
* Name given same as head of self-described private mercenary firm (Adds details)
By Kiyoshi Takenaka
TOKYO, Aug 18 (Reuters) - Japan has received information that one of its citizens has been captured in northern Syria by the Islamic State militant group, the foreign ministry said on Monday.
A video clip posted on YouTube showed a T-shirt clad man lying on the ground being questioned by unidentified persons and responding that he was Japanese and his name was Haruna Yukawa. He also said he was part-journalist, part-doctor.
The name is the same as that of a chief executive of a self-described private mercenary and security firm. No one answered the telephone at the Tokyo-based company.
The Japanese foreign ministry said it was not aware that any group had claimed to be responsible for the capture or of any ransom demand, a ministry official told reporters.
More than 170,000 people have been killed in Syria's civil war, which pits overwhelmingly Sunni Muslim rebels against President Bashar al-Assad, a member of the Shi'ite-derived Alawite minority, backed by Shi'ite militias from Iraq and Lebanon.
"This is an area where various groups are carrying out battle," the foreign ministry official said. "We are focusing on confirming if such a capture has really taken place, as well as the safety of the captured person."
In the video clip, the authenticity of which could not be independently verified, the man can be heard being asked in English, "Why do you have a gun?" But his answer is inaudible.
A Facebook posting by the head of the Japanese security firm on July 11 shows him test firing an assault rifle in what he says is Aleppo, Syria. His Facebook page also shows pictures purporting to be from the Iraqi border. In a series of pictures, he poses in an armoured vehicle and complains of the heat.
Japan's Kyodo news agency quoted an anti-government militant group in Syria as saying Yukawa had entered the country on July 28 and was traveling with that group, hoping to report on the conflict, and was caught up in battle on Aug. 15.
A filing with the Japanese government shows the firm, PMC Japan (Private Military Company) was set up in January and engages in activities ranging from internet homepage design to security business.
The conflict in Syria started when Assad cracked down on a pro-democracy uprising, which then armed itself.
Assad has long painted the uprising in Syria as a foreign-backed Islamist conspiracy and his enemies say he has allowed the Islamic State to grow to promote that idea.
Until this summer, Assad's forces held off from targeting Islamic State, an al Qaeda offshoot formerly known as the Islamic State in Iraq and the Levant (ISIL).
This has allowed the group to thrive and also weaken less hardline opposition groups that are backed by the West.
But this month, Islamic State fighters have gained momentum in Syria, boosted by equipment seized in a rapid offensive in neighbouring Iraq, and the Syrian army has become more confrontational, using air strikes to kill fighters.
(Additional reporting by Nobuhiro Kubo, Kevin Krolicki and Olivier Fabre; Writing by Linda Sieg; Editing by Clarence Fernandez and Jeremy Laurence)