U.S. authorities are investigating claims that an American man fighting for the Islamic State has been killed during clashes in a besieged Syrian town.

Abu Muhammad al-Amriki, who reportedly lived in the U.S. before joining the terror group, has been 'martyred' in the border town of Kobani, according to internet posts by militants.

In a video posted on YouTube in February, a bearded man believed by officials to be the same individual was seen speaking in English with a heavy foreign accent.

Dressed in uniform and clutching a rifle, he said he had lived in America for around 10 years before travelling to Syria to join ISIS. It is unclear whether he was a U.S. citizen.

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Dead? Abu Muhammad al-Amriki (pictured speaking of his U.S. background in a video posted on YouTube in February) has been 'martyred' in the Syrian town of Kobani, according to internet posts by militants

Photos of the fighter, released around the same time as the video, show him posing with an array of weapons, forming the ISIS one-finger salute with his 'brothers' and trying to convert others to Islam.

Now, law enforcement and intelligence agencies are trying to confirm the authenticity of the internet claims about al-Amriki's death, which were posted online by militants last weekend.

Flashpoint Partners, a firm which monitors jihadist Web traffic, said al-Amriki was reportedly killed during recent clashes in Kobani, the Kurdish town on the Turkish border.

The area has been under attack for days by ISIS, which has seized swathes of Syria and Iraq.

Fighter: Photos of the fighter (including this one, with him on the right), show him posing with an array of weapons, forming the ISIS one-finger salute with his 'brothers' and trying to convert others to Islam

In the widely-publicized video, the man believed to be al-Amriki said said he was an al-Qaeda affiliate when he originally arrived in Syria.

However, he later defected to Islamic State after the groups clashed, he said.

According to U.S. officials, at least a handful of Americans - including a Michigan woman and men from Florida and Minnesota - have died fighting in Syria over the past two years.

One of the men, Moner Mohammed Abusalha, reportedly blew himself up in a suicide bombing earlier this year.

Clashes: Flashpoint Partners said al-Amriki reportedly died during recent clashes in Kobani, the Kurdish town on the Turkish border. Above, smoke billows into the air following an airstrike in Kobani yesterday

Patrol: Turkish APC patrols are pictured patrolling the Turkey-Syria border yesterday during the clashes

U.S. and European authorities are deeply concerned about Western foreign fighters in Syria who might return to their home countries to carry out attacks.

It comes as ISIS's sinister black flag has been torn down from a Kobani hill in a symbolic blow against the jihadis.

Kurdish fighters captured the strategic hill of Tel Shair and pulled down the flag that had been fluttering for more than a week.

Symbolic blow: It comes as ISIS's sinister black flag of Islamic State has been torn down from a Kobani hill in a symbolic blow against the jihadis. Above, the flag, that was fluttering for over a week, is seen torn down

Before: A picture taken just over a week ago after the flag had been placed on the hillside by ISIS militants

It followed a sustained stepping up of the U.S.-led airstrikes, with locals counting more than 30 bombs dropped on jihadi positions in just 24 hours.

The fighting in Kobani has forced more than 200,000 people to flee across the border into Turkey, and killed more than 500, mostly fighters from both sides.