Jan Egeland said on Wednesday that thousands of Lebanese civilians remain at risk from unexploded cluster bombs dropped there.
"What's shocking and I would say completely immoral is that 90 per cent of the cluster bomb strikes occurred in the last 72 hours of the conflict when we knew there would be a resolution, when we knew there would be an end."
Egeland said that the UN had assessed nearly 85 per cent of bombed areas in south Lebanon and identified 359 separate cluster bomb strike locations contaminated with as many 100,000 unexploded bomblets.
In Geneva, Chris Clark, head of the UN Mine Action Service in southern Lebanon, said there had been 59 confirmed casualties, including 13 deaths, caused by the explosives since the end of hostilities on August 14.
Egeland said the bombs may have been manufactured in a number of places, including the United States.
"Those places who made those bombs should have a serious talk with Israel on the use of such bombs that are making our lives so miserable trying to help the Lebanese people," he said.
"I hope the US will talk to the Israelis on that, because it is an outrage that we have 100,000 bombs among where children, women, shopkeepers and farmers are now going to tread," Egeland said, adding that he had not been able to get an explanation from the Israelis so far.
"Ninety per cent of the cluster bomb strikes occurred in the last 72 hours of the conflict when we knew there would be a resolution"
Jan Egeland, UN
Egeland said he would launch an appeal for more money for mine clearance when he attends Thursday's conference in Stockholm on Lebanon's reconstruction.
Representatives of more than a dozen organisations are also expected to attend the one-day meeting, the first donors' conference to be held since the Lebanon ceasefire two weeks ago.
The United Nations has asked Israel to provide a list of sites targeted during its month-long offensive in Lebanon, something which is crucial for the clean-up.