The head of a UN agency supporting Palestinian refugees, which is under a corruption investigation, said on Tuesday it still needed $150 million in donations to keep it operating until the end of this year. Pierre Krahenbuhl, commissioner-general of the United Nations Relief and Works Agency, said Switzerland, the Netherlands and Belgium had suspended their contributions to the organization while the UN investigation - on whose findings he promised to act - was underway. "Our (2019) budget for all UNRWA operations in Gaza, the West Bank, East Jerusalem, Syria, Jordan, Lebanon is $1.2 billion. At this moment we have a remaining shortfall of $150 million," Krahenbuhl said. UNRWA provides services to about 5 million Palestinian refugees in Jordan, Lebanon, Syria and the West Bank and Gaza. Most are descendants of some 700,000 Palestinians who were driven out of their homes or fled fighting in the 1948 war that led to Israels creation. Last year the United States, UNRWAs biggest donor, said it was halting its aid of $360 million per year to what it called an "irredeemably flawed operation". Washington has been critical of the United Nations count of Palestinian refugees, questioning a "right of return" claimed by the Palestinians as part of any eventual peace settlement with Israel. In May, US Middle East envoy Jason Greenblatt told the UN Security Council that UNRWA should be effectively dismantled. UNRWAs mandate, which has been repeatedly renewed by the UN General Assembly, runs until June 30, 2020. "The vast majority of countries today are very clear about their support to UNRWAs mandate and their recognition that Palestinian refugees need to continue to be assisted, respected, and see their rights defended," said Krahenbuhl.