Human rights groups on Tuesday warned that escape routes for Iraq's refugees were closing, both inside the country and at its borders.
The warning came as an international conference opened in Geneva to mobilise support for 4m Iraqis forced from their homes – most of them since the 2003 US-led invasion.
The United Nations refugee agency, which organised the conference, said the continuing flood of displaced people, estimated at 40,000-50,000 a month, was putting an intolerable strain on host communities both in Iraq and in neighbouring countries.
António Guterres, UN High Commissioner for Refugees, called on the international community to share the burden of helping an estimated 1.9m people now internally displaced and 2m who have fled to neighbouring countries, primarily Syria (host to 1.2m Iraqis) and Jordan (host to 750,000).
"In the most significant displacement in the Middle East since the dramatic events of 1948 [the creation of Israel], one in eight Iraqis have been driven from their homes," Mr Guterres said. "Host communities are straining under this extraordinary burden, while the suffering of the displaced grows by the day."
As well as financial, economic and technical support, he said, there should be expanded resettlement opportunities for the most vulnerable.
The two-day meeting has brought together ministers and officials from 60 countries as well as the UN and other international agencies.
In a move welcomed by UNHCR officials, Hoshyar Zebari, Iraq's foreign minister, on Tuesday pledged $25m to assist neighbouring countries hosting Iraqi refugees, including provision of basic services. However, from other quarters there were warnings of rising barriers to new refugees seeking safety from sectarian violence and terrorism.
"Jordan and Egypt have pretty much closed their doors to Iraqi refugees, while Syria is shutting out Palestinians trying to flee Iraq," said Bill Frelick, refugee policy director of the US-based Human Rights Watch.
Andrew Harper, head of UNHCR's Iraq Support Unit, told the Financial Times that Jordan and Syria had shown great generosity in taking refugees but that Jordan in particular was "close to the limit of what it could absorb", especially given the scarcity of water resources.
Without international help, school and medical facilities simply could not cope with the sudden influx of Iraqi refugees, he said, noting similar problems for host communities inside Iraq.
The International Organisation for Migration said on Tuesday that half of Iraq's 15 central and southern governates were reported to be turning newly displaced people away unless they could prove they originated there.
The US has offered to resettle 7,000 refugees from Iraq this year and on Monday human rights groups urged the UK to follow suit. However, Mr Harper said UNHCR was no nearer finding a solution for about 15,000 Palestinian refugees in Iraq, who were once protected by Saddam Hussein and are now ostracised and persecuted.
