“They said to me, your dad’s dead. I didn’t believe him,” Wjdan said. “We opened the army’s Facebook page and there were messages saying ‘peace be upon him, he is martyred’.”

Hanan had been told by relatives that Mr Abbas was driving near an oil refinery when an explosion from a rocket, believed to be fired by Isis fighters, ripped through the car he was in.

“A rocket hit my dad’s car. His head exploded – only a small part of him remained.”

Their 18-year-old brother, also a soldier, found his father’s remains, a piece of him about the size of a forearm.

From their living room in Napier, the sisters cried as they watched video footage of their brother pulling at his clothes in despair.

“The way he died is the thing that broke us down. His head being blown off, I don’t think we’ll ever be able to handle it.”

Her father was a tall, muscular man, but his remains weighed just a few kilograms.

Hanan said the family had feared for Mr Abbas when he left for Iraq.

“He wanted to see his family and protect them, and protect others.

“He was trying to free the land from the Isis terrorists.”

Hanan, a registered nurse and Arabic interpreter, said she did not believe Isis terrorists were Muslims.

“There is no religion that accepts women or children should be killed. Isis have never and will never be part of Islam. They are not Muslims,” she said.

Wjdan said her father was a hero: “He died protecting all of us.”

Father of 24 children

Mr Abbas leaves behind 24 children – 12 in Iraq, 12 in New Zealand – including a 5-month-old daughter he had never met.

The Ministry of Foreign Affairs (Mfat) was unable to confirm any details about the incident yesterday, saying it had not been approached by family members.

A spokeswoman said: “Given there is no New Zealand diplomatic presence in Syria or Iraq, the ability of the Government to assist New Zealand citizens requiring consular assistance there is severely limited.”

Mfat advised against all travel to both countries.

Mr Abbas’ daughter Hanan Kadhem Chilab, 24, earlier told the Herald her father had returned to Iraq in June last year to volunteer for a civilian army in the fight against the extremist Islamist group.

“He was our hero,” Ms Hanan Chilab said. “He went there to save the families who were in the battlefield, women and children.

“He was just a normal New Zealander. He was our father. He had an injured leg [from a gunshot wound]. But because the president gave a call to all of the Iraqi people … he signed up and said he wanted to go and fight against the Isis,” she said.

Websites for the volunteer army and Basra community appear to show tributes to their father and pictures of his funeral.

The family’s loss comes after New Zealand-born Karolina Dam, now living in Denmark, revealed this week her son Lukas had been killed after travelling to Syria to fight for the Islamic State.

The Government has urged New Zealanders not to join either side of the conflict in Iraq and Syria. But while it has spoken of sanctions for “foreign fighters” when they returned to New Zealand, it is not clear whether these penalties would apply to New Zealanders who fought against Isis.

Ms Hanan Chilab, a registered nurse and Arabic interpreter, said the family had feared for Mr Abbas when he left for Iraq.

“But he said he can’t stay because he needs to help those women. At that time [Isis] were selling women in Mosul and Tikrit to Syria … and killing their children.

“We thought he was going to come back because he said it’s not going to be that dangerous.”

A YouTube video uploaded on April 5 appears to show Mr Abbas crying at the gravesides of military cadets killed by Islamic State forces near Tikrit, in northern Iraq. His family said he returned to Basra last week and had planned to fly to New Zealand on Sunday.

Ms Hanan Chilab said she had been told by relatives in Iraq that on Friday her father was driving in a convoy of two cars when his car was struck by a rocket – believed to have been shot from Isis fighters – and caught alight.

“The second car stopped. They have only two packets of drinking bottles of water so they tried to put out the car but they couldn’t because the fire was blasting. And Isis were also firing, shooting around my dad’s car and the other car was trying to save my dad.”

His wife, Jamila Abdelsadeh, and two of her sons have travelled to Iraq for the funeral, which would last several days.

Ms Hanan Chilab said the family was overcome with grief. “What fault have we done for all these children to lose their father? He was a great hero. I believe he is a New Zealand soldier, and an Iraqi soldier.”

Waikato University law and war specialist Professor Alexander Gillespie said by sending troops to Iraq, New Zealand had got itself stuck in the middle of a very complex Isis problem.

“There’s no doubt Isis is evil — they’re the fascists of the 21st century, with their regional and global ambitions and their crimes against humanity, but by helping fight them, New Zealand is getting involved in the Middle East in a complicated set of wars.”

Trying to combat Isis was like playing “whack-a-mole”, Prof Gillespie said.

“You shut them down in one place and they pop up somewhere else.

“We could end up fighting all over the world. I believe this is an issue that can only be solved through the United Nations.”

The war against Isis had the potential to be the “next Vietnam”, he said.

“New Zealand entered that war in a non-combat capacity just as we have done in Iraq — and that our involvement does make us more of a terrorism threat,” he said.