Brussels, April 25, 2018 (News Agencies) -- The UN's two most senior Syria experts have warned of an Aleppo-style humanitarian catastrophe in Idlib as an EU donor conference aimed to raise up to $6bn (£4bn)to help Syrians displaced both inside and outside the country. Idlib is the last major territory still in rebel hands. It is partly held by Hay'at Tahrir al-Sham, a jihadi group that Russia and the Syrian government regard as a legitimate target in an area where civilians and fighters continue to pour in as part of evacuation deals in other parts of the country. Jan Egeland, the head of the UN's humanitarian task force for Syria, said: "All my energies currently and in the coming weeks are dedicated to averting a fresh humanitarian disaster." He described Idlib as "one giant area of displacement". "More than half of the population in Idlib of 2 million have already been displaced, sometimes multiple times, so there has to be a negotiated end to the conflict in Idlib. You cannot have a war in the midst of the largest cluster of refugee camps and displaced people in the world," he said. "My fear is the Syrian government will say the place is filled with ‘terrorists' and therefore you can wage war like they did during the sieges in Aleppo and eastern Ghouta ... Yes, there are bad guys wearing beards, but there are many more women and children and they deserve protection. You cannot wage war as if everyone is a terrorist, or else will it be a nightmare." His remarks were echoed by the UN's special envoy on Syria, Staffan de Mistura, who said: "We hope this would be an occasion for making sure that Idlib does not become new Aleppo, the new eastern Ghouta, because the dimensions are completely different." A Syrian government assault on the area is likely to lead to the mass movement of people, possibly toward the Turkish border. Up to 300,000 internally displaced people (IDPs) have reached Idlib province since August, and 700,000 have been displaced across Syria since the start of the year, according to UN figures. Egeland said: "The Syrian civil war has lasted two years longer than the second world war, and far from 2017 and early 2018 becoming a moment when the war wound down, the crisis has escalated. "I really thought 2017 would be the last huge war year, but the crisis has continued at the same ferocity into 2018. This has become a tremendous marathon of pain." The two-day donor conference in Brussels, which is focused as much on the 5 million refugees displaced in neighbouring Jordan, Turkey and Lebanon as the 6 million IDPs in Syria, is the third in a series that began in the UK in 2016. Assad crackdown on Idlib could trigger a refugee ‘catastrophe'