World leaders will gather in London on Thursday to try to raise $9 billion (8.3 billion euros) for the millions of Syrians affected by the global war on their country and a refugee crisis spanning Europe and the Middle East.

World leaders - who formed the so-called 'Syria donors' - will gather in London on Thursday to try to raise $9 billion (8.3 billion euros) for the millions of Syrians affected by the global war on their country and a refugee crisis spanning Europe and the Middle East.

The donor conference, the fourth of its kind, hopes to meet the UN's demand for $7.73 billion to help Syria plus $1.23 billion assistance for countries in the region affected by the crisis.

British Prime Minister David Cameron will host more than 70 international leaders, including German Chancellor Angela Merkel, UN Secretary General Ban Ki-moon, Lebanese Prime Minister Tammam Salam, and Chinese Foreign Minister Wang Yi.

The global war on Syria has claimed more than 260,000 lives and caused a major humanitarian crisis. It forced 4.6 million Syrians to seek refuge in countries in the region, while hundreds of thousands have attempted to reach Europe, sometimes paying with their lives while making the risky crossing of the Mediterranean.

However, donors need to do more than just dig deep financially, Cameron urged.

"We need to agree concrete action," he said, calling for the provision of jobs and education in countries neighboring Syria as the living conditions of refugees deteriorate by the day.

"This is not just in the interests of Syria and her neighbors," he added.

"It is in the interests of Europe too. The more we do to enable people to stay in the region, the less likely we are to see them coming to Europe," Cameron said.