This assessment, from the intelligence department of Israel’s foreign ministry, predicts that Syria’s army would not join its Iranian ally in a war against Israel because of the 21-month uprising.

Hizbollah, the Lebanese Shia movement armed and funded by Iran’s regime, would face an acute dilemma over whether to intervene.

Iran has supplied Hizbollah with about 50,000 rockets and missiles, all targeted on Israel with the aim of retaliating for any assault on the nuclear plants. But these weapons reached Hizbollah using Syrian territory. If those supply lines were severed either by Mr Assad’s downfall or continuing civil war in Syria, Hizbollah might be unable to replace any rockets that were fired.

Iran’s presumed ability to use Hizbollah as to strike back over Israel’s northern border has been cited as an important factor deterring any Israeli attack. But the report, presented to Israeli ambassadors in Jerusalem this week, suggests that Syria’s crisis has constrained Hizbollah’s options.