But one Chinese national claims to have entered Syria to join the Kurdish militia group, the Popular Protection Units (YPG), one of the largest groups fighting against IS.

The YPG is a key ally of the US-led international coalition against IS, and has driven the militants from several Syrian border towns this year, backed by coalition airstrikes.

Ba Si Pan, as he calls himself, may be the first Chinese national fighting IS in Syria with the YPG. He won't reveal his full name, but says Ba Si is his name in Kurdish.

The 25-year-old says he has fought on the frontline in Kobane twice.

Yet when I spoke with him by phone, he sounded calm and composed - despite not speaking any English or Arabic, and having to communicate with fellow fighters with an electronic dictionary.

'Innocent lives'

Mr Pan said that he joined YPG purely because he wanted to help in the fight against a common enemy of humanity.

"IS has taken so many innocent lives", and he feels some responsibility to help defeat them, he says.

In his account, which could not be independently verified, Mr Pan, who is ethnic Han Chinese, says that IS has "trained many Chinese people and then sent them back to China".

Chinese authorities claim that some ethnic Uighurs who have fought alongside IS in Syria and Iraq have returned to China with plots to launch attacks in the country.

However, this claim has been disputed by exiled Uighur groups.

Based in China's south-west Sichuan province, Mr Pan said he didn't have a proper job back home, and recently split up with his girlfriend.

He says he received some civilian military training in Sichuan in 2012, so he is convinced he is able to do some real fighting.

On 24 September, he took a Turkish Airlines flight to Istanbul, from Bangkok, according to his flight records seen by the BBC. He told me he eventually entered Syria via Turkey in October.

Some governments, including the UK, have warned their citizens that taking part in the conflict in Syria and Iraq could amount to an offence.

The Chinese government has never specified whether it is legal for its citizens to enter Syria to fight. However, its embassy in Syria has urged citizens not to travel in Syria.

The YPG is made up mainly of Kurdish fighters, but it describes itself as a multi-ethnic and multi-nationality institution.

By June this year, more than 400 foreign fighters, mainly from Australia, the US and Europe, had joined the YPG, according to the Syrian Observatory for Human Rights.

"[YPG] has a very active online campaign, trying to recruit people, and the message is shouted out in every direction," says Raffaello Pantucci, International Security director at London's Royal United Services Institute (RUSI).

However, Mr Pan isn't the first ethnic Chinese man to fight IS.

One of the most popular YPG fighters on the Chinese internet is Huang Lei, a British Chinese volunteer who attracted ample attention from Chinese media in May, and has since become an online celebrity of sorts.

Mr Pan says he was inspired by Huang Lei's story. "I had actually thought he is still here in Kobane, but when I arrived in Kobane I was told he's already back in the UK."

Since joining the YPG, Mr Pan has also occasionally engaged with social media via WeChat and China's weibo microblogs, uploading pictures of himself in military uniform and posing with automatic weapons.

Sometimes he sounds rather disappointed; at other times he appears to be enthusiastic and proud.

In one of his first messages sent in October, he wrote: "I have to acknowledge that IS's equipment is much better than that of YPG's… But no matter how difficult it is, I believe justice will eventually triumph."

Many Chinese social media users have called Mr Pan a "hero" - but others have expressed concerns for his safety, or urged him to blur his face online to avoid reprisals from IS.

Although the YPG is one of the largest and strongest groups fighting against IS, the risks remain high.

In March, a 19-year-old German woman Ivana Hoffman was killed battling IS. And last month, IS killed a Chinese national Fan Jinghui, prompting an angry response from the Chinese government.

However, Mr Pan sounds undeterred. "Now that I'm here, I don't worry," he said, "I will simply do my best to protect myself."

(BBC)