The UN's humanitarian chief has accused Israel of "completely immoral" use of cluster bombs in Lebanon.
Cluster bombs are causing injuries and deaths daily, the UN says
UN clearance experts had so far found 100,000 unexploded cluster bomblets at 359 separate sites, Jan Egeland said.
Israel has repeated its previous insistence that munitions it uses in conflict comply with international law.
Earlier, Israeli Prime Minister Ehud Olmert rebuffed UN chief Kofi Annan's calls for a swift end to Israel's air and sea blockade of Lebanon.
After talks with Mr Annan, Mr Olmert said the siege would only be lifted once the ceasefire terms were fully implemented.
This included the release of two Israeli soldiers whose capture by Hezbollah militants sparked the conflict.
But a Lebanese Hezbollah cabinet minister said there would be no unconditional release of the soldiers - the pair would only be freed as a result of a prisoner exchange with Israel.
UN efforts to rid Lebanon of cluster bombs have been under way since the conflict ended. Earlier estimates from UN experts had suggested a total of about 100 cluster bomb sites.
Mr Egeland described the fresh statistics as "shocking new information".
"What's shocking and completely immoral is: 90% of the cluster bomb strikes occurred in the last 72 hours of the conflict, when we knew there would be a resolution," he said.
The UN ceasefire resolution which ended the month-long conflict between Israel and Hezbollah was agreed by the Security Council on Friday, 11 August, and came into effect on Monday, 14 August.
Mr Egeland added: "Cluster bombs have affected large areas - lots of homes, lots of farmland. They will be with us for many months, possibly years.
"Every day, people are maimed, wounded and killed by these weapons. It shouldn't have happened."
Mr Egeland said his information had come from the UN Mine Action Co-ordination Centre, which had undertaken assessments of nearly 85% of the bombed areas in Lebanon.
Earlier this week the US state department launched an inquiry into whether Israel misused US-made cluster bombs in Lebanon during the conflict.
A senior White House official told the BBC that the investigation would focus on whether US-made weapons were used against non-military targets.
At their talks in Jerusalem, Mr Annan and Mr Olmert discussed the deployment of UN troops in Lebanon as well as the continuing blockade.
The UN chief said he hoped Israel would withdraw from southern Lebanon once 5,000 UN peacekeepers were on the ground "in the coming days and weeks".
The BBC's Jill McGivering, in Jerusalem, said Mr Annan and Mr Olmert emerged from their meeting with little sign of the gap between them having narrowed.
Mr Annan's Jerusalem talks followed a visit to Lebanon as part of a regional tour aimed at bolstering the truce between Israel and Hezbollah.
After his talks in Israel, Mr Annan flew to the West Bank for talks with Palestinian Authority President Mahmoud Abbas.
At a joint press conference in Ramallah, Mr Annan said that more than 200 Palestinians had been killed since the end of June, and the violence had to stop.
Mr Annan has now arrived in Jordan for talks with King Abdullah II, after which he is expected to proceed to Syria.