President Joe Biden is said to be privately fearing a potentially 'catastrophic escalation' as the Israeli government plans a retaliatory attack on Iran.

Iran bombarded Israel with hundreds of missiles and drones on Saturday in response to a drone strike in Syria that killed 12 Iranians, including two top generals. 

The strike marks the first time a direct military assault has been launched by Tehran on Israel - despite decades of enmity dating back to the country's 1979 Islamic Revolution. 

Senior US defense officials have told NBC News that they worry an Israeli response to the attacks would be 'frenetic' and 'catastrophically escalatory'. 

Three senior administration officials have also told NBC that Biden had privately expressed concern that Netanyahu is trying to pull the US into the conflict. 

Biden spoke with Israeli Prime Minister Benjamin Netanyahu in a late-night phone call on Saturday and made it clear that US forces would not participate any further.

Republican hopeful Donald Trump, however, has instead vowed that he would 'make Iran pay' for the attack - and claimed that such an escalation on the world stage would have never happened in the first place if he was in the Oval Office.

Biden has urged Netanyahu not to respond to the attacks by retaliating against Iran. The Israeli Prime Minister's war cabinet is in favor of a reaction - but is divided over the timing and scale of any such response, according to reports.