Iran's $6-billion fund unfrozen by the United States and transferred to its bank account in Qatar as part of a prisoners swap between Washington and Tehran last month will remain on hold, according to United States and Qatari officials.

Iran said the US "can not renege" on an agreement to transfer the funds through mediator Qatar following the bloody assault on Israel by Hamas which Tehran financially and militarily supports.

Hamas, has come under intense scrutiny since fighters of the Islamist group stormed across Israel's southern border at the weekend, shooting people in their homes and on the streets in an onslaught that claimed more than 1,200 lives.

Iran has insisted it was not involved, but celebrated the Hamas attack as a "success."

The Washington Post reported Thursday that a decision was made to halt access to the funds, while President Joe Biden faces rising pressure on the matter given concerns over Iran's connections to Hamas.

US officials said earlier that they had not seen any intelligence to show Iran was involved in planning or preparing the Hamas attacks.

"We have strict oversight of the funds and we retain the right to freeze them," US Secretary of State Antony Blinken told a press conference in Tel Aviv on Thursday.

The White House added in a separate briefing that "every single dime of that money is still sitting in a Qatari bank."

"Not one dime of it has been spent," according to National Security Council spokesperson John Kirby, adding that the US is watching the account closely but refusing to speculate about "future transactions."