Over a shaky mobile phone connection, the voice of a brother Yusuf had not seen in years is heard from across the Syrian border.

Money is low and his family need more. But Western Union does not deliver to Raqqa, the de-facto capital of the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) and the city closest to the village where Yusuf's parents and siblings still live.

A defector from the Syrian army, Yusuf, who is using a pseudonym for security reasons, fled to the Turkish city of Antakya two years ago, where he found work with an international NGO. Each month, he sends at least $500 back home, relying on a network of money traders operating through applications such as WhatsApp - and often blind trust.

"Now, you rarely find a family inside Syria without one or two of their family members outside, sending money," Yusuf told Al Jazeera.

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After five years of war, more than 13 million people in Syria are in need of aid, and remittances have become a critical lifeline. But outside regime-held areas, formal banking and money transfer services have long since shut down.

Everyone from refugees to international NGOs now rely on the hawala system, a centuries-old tradition of money transfer. Through a network of traders on either side of the border, funds from abroad are swiftly transferred into rebel-held areas and even besieged cities.

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Yusuf's 20-year-old brother, who was about to finish school when Syria's war broke out, now cares for his family and helps to farm their patch of land. But the cost of seeds and diesel have skyrocketed, and without the money Yusuf sends, they would struggle to survive.

"I worry about my brother; he's a young man and ISIS is trying to ask people to serve in their army," Yusuf said. "He's terrified to stay there, but he's minding the family."

For money to reach Raqqa, it may pass through several traders in territories controlled by different armed groups. Yusuf is charged around $20 for each transaction.

Recently, hawala traders in Antakya told him that they could only transfer to opposition-held areas. Desperate to get money across, he called a friend in Sanliurfa, a Turkish city opposite Raqqa. That night, his friend headed to a local jewellery shop - barbers, grocers, jewellers and phone shops often double as informal hawala offices - with $400 he had cobbled together.

The trader charged a small fee, sent a WhatsApp message with a name and amount, and the money was ready to collect. The next morning, Yusuf's brother set off on a motorcycle to Raqqa, collecting a handful of bills.

"It's dangerous going there, but that is the only way," Yusuf said.

It's a kind of solution. If someone can't transfer the money, my friend [in Syria] starts thinking, 'I have a family, a child.' He starts thinking, 'Where can I earn the money?'

Rami Sharrack, Syrian Economic Forum

When Syria's uprising began in 2011, banks shut down branches in areas hostile to the regime - proof of the "close-knit link" between the financial sector and the regime, said Rashad al-Kattan, a political and security risk analyst with the Centre for Syrian Studies at the University of St. Andrews. 

"It wasn't a security issue; it was more part of the Syrian regime's policy to punish those communities and exclude them from the financial banking sector - part of the wider spectrum of sieges and starvation," Kattan told Al Jazeera. 

A pediatrician working in a hospital in Idlib province told Al Jazeera on condition of anonymity that transferring money to opposition-held areas is a matter of life or death.

"Getting cash into Syria is particularly difficult due to security concerns, yet you can't do without it," he said. "We have to buy diesel to run generators, and this alone could bring the hospital to a standstill."

In his village, Yusuf says there is no work, and fighting with an armed group is well paid. The more extreme groups offer the highest salaries. A recent investigation by International Alert found that fighters with Jabhat al-Nusra, which at the time of the report was affiliated with al-Qaeda, were paid between $300 and $400 a month, while the Free Syrian Army offered around $100.

In an airy office in Gaziantep, a metropolis in southern Turkey, Rami Sharrack of the Syrian Economic Forum noted that the hawala system, criticised as an easy funding channel for armed groups, can actually discourage people from joining these groups.

"It's a kind of solution," Sharrack told Al Jazeera. "If someone can't transfer the money, my friend [in Syria] starts thinking, 'I have a family, a child.' He starts thinking, 'Where can I earn the money?'"

In areas outside government control, where humanitarian needs are critical, unregistered hawalas have been used by NGOs as the only "scalable cash-out facility", according to the Norwegian Refugee Council. Thirteen humanitarian agencies surveyed by Beechwood International estimated that $16m was transferred in cash into Syria in 2014 alone.

With millions of refugees from Syria sending money home, the hawala trade is booming, Sharrack said, noting that his own cousin last year sent $2,000 to his father in Syria through hawala from the United Kingdom.

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In downtown Gaziantep, men bustled for space in the cream-walled office of a Syrian-run hawala business, thumbing through wads of dollar bills. Behind the polished wooden counter, money-counting machines whirred hungrily.

During the month of Ramadan, the company transferred more than $150,000, sending at least 50 transfers a day to Syria. Humanitarian organisations and media use the office to send salaries to employees in Syria.

A soft-spoken 26-year-old in jeans and black-rimmed glasses, Mohammad Fareed, an electrical engineering graduate from Aleppo, fled Syria two years ago and works as an accountant for the company.

It's more difficult in Assad's cities. If they see American dollars in Syrian people's hands, it's a big problem.

Mohammad Fareed, accountant

"The amount of money supporting families is small," he told Al Jazeera, noting there are also concerns about funds being diverted to armed groups, but the company refuses to transfer to ISIL-controlled areas. Due to inflation, they deal mostly in US dollars, although the use of foreign currency is banned in regime areas.

"It's more difficult in Assad's cities," Fareed said. "If they see American dollars in Syrian people's hands, it's a big problem."

Every month, Fareed sends money to his uncle in Aleppo - a transfer that was simple before the recent siege. Some areas became impossible to reach, even for hawala traders, as demand spiked along with food and fuel prices. Some independent traders in Aleppo started charging a five percent commission, but it was the only way to get money in.

"We are forced to send it," Fareed said. "To support people and to help families, it's very important." 

Source: Al Jazeera