Israel's ambassador to the UN has accused Iran of paying Hamas $50m to block the release of an Israeli soldier captured by Palestinian militants.
Cpl Shalit was captured by Palestinian militants in late June
The ambassador in New York, Dan Gillerman, made the claim without giving any further evidence or details.
The payment, which Iran denies making, allegedly went to the head of Hamas' political bureau Khaled Meshaal.
The soldier, Cpl Gilad Shalit, was captured in June in a cross-border raid from Gaza by Palestinian militants.
Israel intensified its military campaign in Gaza following his capture in June, and the strip has been cut off from the outside world for long periods of time.
Hamas, the militant group that runs the Palestinian Authority, says that in return for freeing Cpl Shalit, Israel must release some of the several thousand Palestinians held in its jails.
Since the end of June 2006, more than 300 Palestinians have been killed in Israeli army operations in Gaza and the West Bank, according to Israeli human rights group B'Tselem.
On Thursday, the Israeli daily newspaper Yediot Ahronot reported that a deal on Cpl Shalit's release was foiled when an Iranian delegation met Khaled Meshaal in Damascus and offered him $50m (£26.6m). Mr Meshaal apparently accepted the money and hardened the conditions attached to Cpl Shalit's release.
In an open session on the Middle East at the UN Security Council on Thursday, Mr Gillerman said of the reported payment: "if this is the way in which Iran threatens humanitarian situations, I shudder to think about the lengths to which Iran will go to undermine a diplomatic one, and achieve its dangerous regional aspirations and nightmarish and megalomaniacal dreams of nuclear capability."
He went on to tell reporters at the UN: "We have every reason to believe that the Iranian regime has bribed Khaled Meshaal. I cannot divulge the sources or give you any further details on this."
Mr Gillerman said the aim of the Iranian payment was "to sabotage the negotiations on the release of Corporal Gilad Shalit and prevent his release".
Iranian diplomat Mansour Sadeghi told the council that his government "categorically rejected" the allegations.