The European Union's top diplomat says the EU expects "significant pledges" for Syria at a donor conference, as the bloc seeks to keep the 8-year conflict in the international spotlight.

Speaking ahead of Thursday's donor conference in Brussels, foreign policy chief Federica Mogherini said that Syrians must "not to be forgotten in a moment where the international community seems to care a little bit less about this."

Around 55 countries and 80 delegations are expected to attend.

The U.N. says $3.3 billion is needed to help meet Syria's aid needs, plus a further $5.5 billion to support countries like Jordan, Lebanon and Turkey, where many Syrians have sought refuge.

About 11.7 million Syrians still depend on aid and some 6 million people have fled the country.