Failure to help Syria "get back on its feet" will result in a fresh wave of outward migration, the head of the International Committee of the Red Cross warned Monday, as the EU hosted a donor drive for the war-torn country.

More than 300,000 refugees have returned to Syria hoping to start over following the ouster of Bashar al-Assad, according to the United Nations.

But the situation in the country is fragile, with outbursts of violence and the conflict's legacy of destruction making aid all the more indispensable, said ICRC president Mirjana Spoljaric.

"When you don't have schools for your children, when you don't have functioning hospitals, when you don't have access to water and energy, when your house is still collapsed and you don't have the means to rebuild [it], you will be forced to leave," she told AFP in an interview.

Spoljaric was in Brussels for an annual donor conference, which for the first time saw Syrian authorities represented — with interim foreign minister Assaad al-Shibani in attendance.

Western and regional powers are hoping to help put Damascus on the road to stability after 14 years of civil war that have sent millions of refugees over its borders.

But this month the worst outbreak of deadly violence since Assad was toppled in December rocked confidence in the new Islamist-led authorities.

"Syria is at the crossroads," Spoljaric said, adding that peace and stability were "possible" but required "a lot of attention" from the international community.

The country's needs are massive as swathes lie in ruins and the economy has been ravaged by years of international isolation after Assad's 2011 crackdown on opposition sparked the civil war.

Spoljaric did not provide a figure but said she hoped the conference would produce funding and political commitment to help the new authorities rebuild "a functioning economy, which at the moment is not existent".

"The hospital system, or the health system, has largely collapsed. We are at less than half of what was available in terms of medical assistance in 2011. The same applies to energy and water and education," she said.

"If we want people to be able to stay or to come back if they wish, we have to support them in building the environment that would allow them to live and live in a dignified way."

The ICRC budget for Syria for 2025 is only about 14 percent funded so far, she noted.

The group has like others been impacted by President Donald Trump's decision to order a suspension of U.S. foreign aid but it is "engaging" with Washington to continue cooperation, Spoljaric said.

Money was needed among other things to support efforts to determine the fate of tens of thousands of detainees and others who went missing during the war.

"The healing of a country cannot happen if the missing files are not resolved," Spoljaric said.