For months, employees of the International Committee of the Red Cross have made weekly visits to a detention camp in northern Syria bearing a photograph of a petite woman in her early 60s.

They show the image to camp officials, comparing it with pictures of tens of thousands of other people in the camp’s database.

All of them are escapees from the Islamic State’s last stretch of territory, which fell to US-backed forces last month.

The woman in the photo is Louisa Akavi, 62, a New Zealand nurse and midwife who was abducted in late 2013 in the north-west Syrian city of Idlib. She is one of the last links to the group of at least 23 Western hostages held by ISIS, a majority of whom were released for ransom, while others were killed in widely publicised beheadings.

For more than five years, her employer and her government imposed an especially strict media blackout, warning that any mention not only of her identity, but even of her nationality, could endanger her.

But now that ISIS’s caliphate has collapsed, the aid group has broken its silence in hopes that the public can help find her and two Red Cross drivers, both Syrians, kidnapped alongside her.

“From the moment Louisa and the others were kidnapped, every decision we made was to maximise the chances of winning their freedom,” Yves Daccord, director-general of the humanitarian organisation, said in his first interview about his missing colleagues. “With the Islamic State group having lost the last of its territory, we felt it was now time to speak out.”

The aid group and the New Zealand government have reason to believe she is alive. As recently as December, Red Cross officials said, at least two people described seeing her at a clinic in Sousa, one of the final villages to be held by ISIS.

The Red Cross also considers credible at least three other reported sightings of her – at Abu Kamal in 2016, Raqqa in 2017 and Mayadeen last year, officials with the aid group said.

Some of the witnesses said they saw her performing medical duties at clinics and hospitals under ISIS control, indicating that she was no longer held in a cell and was able to use her nursing skills to win a modicum of freedom, according to Mr Daccord.

Current and former US intelligence officials, as well as government officials in New Zealand, speaking on the condition of anonymity, said there were strong indications that she was alive last year, based on sightings.

The US officials also said Ms Akavi might have been held with a British hostage, journalist John Cantlie, at Mosul University in neighbouring Iraq, before the area was liberated in late 2016.

Based on the intelligence indicating that Ms Akavi was still alive, New Zealand deployed special forces to Syria to search for her, Foreign Minister Winston Peters said in a statement on Monday.

The “non-combat” team, which has included members from the New Zealand Defence Force and the Foreign Ministry staff, is authorised to visit Syria “from time to time”, Mr Peters said. “The efforts to locate and recover Louisa are ongoing.”

Ms Akavi would be the longest-held hostage in the 156-year history of the International Committee of the Red Cross, the group said.

Her ordeal began in late October 2013, when she traveled to Idlib to deliver medical supplies. Three days later, she and six colleagues were returning to Damascus in a convoy marked with the Red Cross emblem when gunmen stopped them at a checkpoint. Four of the aid workers were freed the next day, but Ms Akavi and two others, Nabil Bakdounes and Alaa Rajab, remain missing.

Mr Daccord was immediately alerted to their disappearance, and a 15-member Red Cross team, including a crisis group in Geneva, began looking for them.

“I was convinced she’d be back soon – 24 hours, 48 hours, a week,” said Avril Patterson, a colleague of Ms Akavi’s who arrived in Damascus a day after her friend’s disappearance. “And then as time goes on, your denial doesn’t work any more.”

At first, the Red Cross did not know the identity of the captors. But then, a school near the checkpoint where the workers were taken was painted with the ISIS logo.

Months later, in phone calls, emails and text messages, the terrorist group negotiated with the Red Cross, initially demanding a ransom of less than €1 million (under $1.58 million) and calling for the release of detained ISIS fighters. But the ransom fluctuated as time went on, the aid group said, rising to €20 million ($31.6 million) before dropping to €5 million ($7.89 million), the amount requested for several other Western hostages.

In those exchanges, the Red Cross was able to send proof-of-life questions, asking for the number of Ms Akavi’s insurance policy, which her family said was written on a card the nurse kept with her. ISIS provided the correct number, one of several personal questions the group answered that convinced the Red Cross it was in fact speaking to her captors, Mr Daccord said.

By early 2014, the aid group confirmed that Ms Akavi was being detained in a facility next to an oil installation outside Raqqa.

She shared a cell with an American aid worker, Kayla Mueller, according to the aid group and others who were in the same jail. An adjacent cell held more than a dozen male prisoners from Europe and North America, including American journalist James Foley, as well as Cantlie, the only other Western hostage who may still be alive, according to a statement in February by a British government official.

By mid-2014, ISIS had released most of the hostages after their governments, and sometimes their employers or families, paid multimillion-dollar ransoms. But three British and four US citizens, whose governments hew to a strict no-ransom policy, remained behind, along with Ms Akavi.

That August, after failing to get a ransom for his release, ISIS killed Foley. His beheading, and the similarly brutal deaths of two British hostages and the remaining American men in the next few months, shocked the public and rattled the Obama administration. That set in motion a military intervention in Syria that ended just weeks ago with the collapse of ISIS’ rule.

The female prisoners were initially spared, even though ISIS sent the Red Cross an email in July 2014 saying it planned to execute both Ms Akavi and Ms Mueller as retaliation for a failed rescue attempt by US commandos, according to Mr Daccord.

By autumn, the women were sharing their cell with two Yazidi teenagers who had been abducted with thousands of other women in Iraq to be used as sex slaves.

“They took us to Raqqa and put us in a jail – that’s where we met Kayla and Louisa,” recalled one of the teenagers, D, who asked to be identified only by her first initial. “Louisa was old. She said her hand was hurting,” said D, now 19, who was interviewed in 2015 at a refugee camp in Iraq after escaping.

An Islamic State jail in Raqqa, Syria on June 12, 2018. Photo: Ivor Prickett/New York Times

In late 2014, ISIS stopped responding to the Red Cross’ messages, and there was no news of Ms Akavi in 2015, officials with the aid group said.

But in 2016, they received a tentative confirmation that a foreign woman matching her description had been spotted in Abu Kamal, a town in Syria where the group’s fighters had retrenched.

Then, in what Mr Daccord called “a breakthrough,” several people who had escaped to detention camps in Iraq in late 2017 told Red Cross workers they had been treated by Ms Akavi in Syria.

“This was incredible information to receive, apparent confirmation of her location, that she was still alive and that she was still doing what she is trained to do and has long done: Providing medical care in a conflict zone,” Mr Daccord said.

Among the strongest evidence that she was still alive came just four months ago, when two people interviewed by the Red Cross confirmed seeing her working as a nurse in Sousa.

But since then, there has been no reported sighting.

Tens of thousands of ISIS supporters – including fighters and their wives and children – poured into the desert in the final weeks before the group’s last toehold was liberated.

The women are being held behind a chain-link fence at the al-Hol detention camp. The sprawling tent city has been described as a “mini-caliphate” with ISIS wives patrolling the area, threatening women who do not cover their faces.

On weekly trips, Red Cross workers are checking the camp for Ms Akavi. They worry she may be inside and fearful of identifying herself because of possible repercussions from ISIS loyalists there.

And so, a few weeks ago, a senior Red Cross official travelled to the camp with one mission: Erect a tall Red Cross flag amid the tents. It is intended to be a beacon of sorts for Ms Akavi, encouraging her to approach her colleagues and seek refuge, if she is there.

“There is a chance that it will reach her,” Mr Daccord said.

-The New York Times