International donors are today expected to pledge billions of dollars for Syria after the UN's special envoy warned of a looming humanitarian disaster in the rebel-held region of Idlib.

The UN's aid agency says some $8bn is needed from the gathering of ministers and aid organisations in Brussels for work both inside Syria and with refugees in neighbouring countries.

The conference will also try to re-energise the floundering UN-led peace process in the hope of ending the war, which is now in its eighth year.

Idlib, on the Turkish border in northwestern Syria, is held by an array of rebel, Islamist and jihadist forces and has seen an massive influx of people fleeing the conflict.

"We were and are concerned on the humanitarian side by Idlib. Because Idlib is the big new challenge, 2.5 million people," UN Syria envoy Staffan de Mistura told the first day of the conference yesterday.

"We hope that this would be an occasion for making sure that Idlib does not become the new new Aleppo, the new Eastern Ghouta, because the dimensions are completely different."

The head of UN aid agency UNOCHA Mark Lowcock said the gathering needed to raise some $8 billion for work inside Syria and with refugees in neighbouring countries, warning that some programmes may have to be cut back if funds are not forthcoming.

"We are quite desperately short of resources," he told reporters, saying UNOCHA managed to raise only half of the funds it needed in 2017.

Europe is also keen to use the conference to restart UN-led talks in Geneva, which have made little progress in eight rounds.

President Assad's government has paid little interest in the UN talks with Russia, Iran and Turkey launching a rival process in the Kazakh capital Astana last year.

Russia and Iran are Mr Assad's key allies and their military intervention in Syria is widely seen as tipping the balance in the civil war.