The United States has briefed Israel on the details of its back-up plan for a military strike on Iran in the event that diplomatic efforts to halt the Islamic Republic’s development of nuclear weapons fail, Haaretz reported Sunday.

According to an anonymous senior American official, White House National Security Adviser Tom Donilon informed Prime Minister Benjamin Netanyahu during a meeting earlier this month that the US is preparing in earnest for the possibility that diplomatic efforts to halt Iran’s unsanctioned nuclear program fail.

To demonstrate this, and perhaps to dissuade Israel from striking Iran on its own, Donilon outlined the US’s plan for striking Iran’s nuclear sites, and gave a detailed overview of the weapons capable of destroying them.

Earlier this week US Air Force Secretary Michael Donley announced the combat readiness of the Massive Ordinance Penetrator, a 15 ton bunker buster capable of penetrating up to 200 ft underground. Such a weapon could be used to attack Iran’s heavily fortified, subterranean nuclear facilities in the event of a military assault.

“We continue to do testing on the bomb to refine its capabilities, and that is ongoing,” Donley said. “We also have the capability to go with existing configuration today.”

“If it is necessary to use it today, we are ready to do so,” Donley said.