A 19-year-old German woman who joined Kurdish fighters battling Islamic State militants in Syria has been killed, according to a monitoring group.

The Syrian Observatory for Human Rights (SOHR) said on Monday that the woman, who has been named as Ivana Hoffman, died during clashes in the Tal Tamr region of Hasakah province in northeast Syria.

Hoffman, who was a member of Turkey's Marxist-Leninist Communist Party (MLKP) and fighting as part of the Kurdish People's Protection Units (YPG), had taken the nom de guerre Avasin Tekosin Gunes and been in Hasakah province for six months, according to an MLKP statement quoted in German media. The statement added that she fought "until the last bullet" defending a position from an ultimately unsuccessful Islamic State attack.

The MKLP, which announced commemoration events for the German fighter it hailed as an immortal "pole star", says it has been sending volunteers to fight with the YPG for some time.

Hoffman is the third westerner known to have died in the ranks of the YPG. Two others, British former Royal Marine Konstandinos Erik Scurfield and Australian Ashley Johnston were killed in Hasakah on March 4 and February 25 respectively.

Hoffman was the first woman to lose her life, but her presence in the YPG would not have been abnormal — around one third of YPG fighters are women, who fight alongside men in combat roles.

In a video said to show Hoffman soon after her arrival in Syria, she is seen speaking German and brandishing an assault rifle with her face obscured by a scarf.

Meanwhile, a dispute over the events surrounding a "friendly-fire" incident that killed a member of the Canadian special forces in neighboring Iraqi Kurdistan continues.

Sgt. Andrew Joseph Doiron died and three others were injured on Friday after Kurdish peshmerga fighters fired on them as they approached a checkpoint. They were the first Canadian casualties in the US-led coalition battling the Islamic State.

Kurdish officials said the peshmerga shot at a group of Canadian soldiers when they turned up at a front line position to direct airstrikes without warning. Peshmerga spokesman Brig. Gen. Halgurd Hikmet said the Canadians arrived at Bashiq village in Nineveh province unannounced. "When they returned, the peshmerga asked them to identify themselves... They answered in Arabic, that's when peshmerga started shooting. It was their fault," Hekmat told the Associated Press. "I consider it an improper action by the Canadians, and illogical," he added.

However an unnamed Canadian military official also cited by AP said the soldiers had returned to an observation point where they had been earlier in the day and had previously arranged signals and an approach procedure with the peshmerga; they had also passed through two nearby checkpoints on their approach. "They got lit up by one guy for reasons that are unknown to us," the official said. "Once he started shooting, some other fellows from the Kurds engaged and that's when the injuries occurred."

Canada sent 69 special forces troops to Iraqi Kurdistan last year. They were originally deployed as a non-combat force, but are now working with the peshmerga in a role that authorities describe as providing assistance and advice. This involves directing air strikes from front lines positions but has included at least one incident where Canadians returned fire after coming under attack by Islamic State fighters.

The weekend saw heavy coalition airstrikes on Islamic State targets, including in an attack that hit an oil refinery near the Turkish-Syrian border town of Tel Abyad. Video said to be from the immediate aftermath shows a huge fireball rising into the night.

SOHR said around 30 died in the attack.

Another local activist group, Raqqa is Being Slaughtered Silently, said that around 14 fighters were killed.

The Islamic State relies on black market oil sales to fund itself and supply the large part of Syria and northern Iraq under its control. The coalition has made targeting this infrastructure and other sources of income a priority.