US Keith Broomfield killed Syria
US national Keith Thomas Broomfield was killed in SyriaFacebook

A US national has died fighting alongside Kurdish militias against the Islamic State (Isis) jihadi group Syria.

Keith Thomas Broomfield was killed in combat in the civil war-torn country, where he had joined Kurdish YPG forces a few months ago, NBC News reported, and quoting officials and relatives.

Broomfield's mother, Donna, told the broadcaster she was aware her son had died during clashes with IS militants.

"I didn't want him to go but I didn't have a choice in the matter," the woman from Westminster, Massachusetts told NBC News. "I'm waiting for his body to come back."

The YPG said the 36-year-old was killed on 3 June near Kobane, the northern Syrian city that became a symbol of Kurdish resistance after an IS siege was repelled earlier this year, after more than four months of fighting.

Although numerous US nationals are known to have travelled to Syria to fight IS, Broomfield is believed to be the first American to die there. His demise was confirmed by the US State Department.

The news came as the White House announced an additional 450 troops were to be sent to fight the Islamist group in neighbouring Iraq.

The military personnel will not serve in a combat role but boost the training of local forces after the spectacular debacle of Ramadi, the capital of Anbar province, which fell to IS in May despite government forces outnumbering the attackers.

The fall of the city drew severe criticism from the US, with Defence Secretary Ashton Carter saying it showed Iraqi forces had "no will to fight".

The additional forces will add to the 3,100 US troops already deployed in Iraq.

"These new advisors will work to build capacity of Iraqi forces, including local tribal fighters, to improve their ability to plan, lead, and conduct operations against ISIL [another name for IS] in eastern Anbar," the White House said in a statement.