The Lebanese group is moving faster than Iran in its planning and is looking to strike Israel in the coming days, one of the sources told CNN.

Iran, meanwhile, appears to still be working out how it plans to respond, multiple officials have told CNN. 

Hezbollah's chief Hassan Nasrallah said Tuesday his group and Iran were "obliged to respond" to Israel "whatever the consequences" after the assassinations last week of Hezbollah military commander Fouad Shukur and Hamas leader Ismail Haniyeh.

Hezbollah will retaliate "alone or in the context of a unified response from all the axis" in the region, "whatever the consequences," Nasrallah added.

One US military official told CNN that Iran had made some, but not all, of the preparations that the US would expect to see in advance of a major attack on Israel.

However, Hezbollah could act with little to no notice given Lebanon’s proximity to Israel as its direct neighbor to the north, the second source familiar with the intelligence said.

It is not clear how or if Iran and Hezbollah, are coordinating on a possible attack right now, the source added, and there is a sense among some officials that the two may not be entirely aligned on how to move forward.

Israel last week acknowledged killing Hezbollah commander Fouad Shukur in a strike in Lebanon.

Bur while it did not publicly comment on Haniyeh's assassination, Israel informed US officials that it was behind the assassination of Hamas leader, immediately after Iran announced his death on 31 July, the Washington Post reported.

"White House officials responded with surprise and outrage to Haniyeh’s assassination, which they saw as a setback to their months-long quest to secure a ceasefire in Gaza, which is a fitful process they believed was making progress," three people familiar with the White House’s thinking told Washington Post.

An Israeli official confirmed that a call between US President Joe Biden and Israeli Prime Minister Benjamin Netanyahu last week, after Haniyeh’s death, was “tense".