Against a background of friction between the US and Israel over thwarting Iran’s nuclear drive, Washington says it will scale down its participation in what was planned to be the largest ever joint Israeli-American military exercise, Time Magazine reported Friday.

The Austere Challenge 12 exercise, to be held in October, was to feature thousands of soldiers and advanced anti-missile defense systems and simulate simultaneous fire from Iran and Syria.

But the report quoted sources in Washington as saying only 1,500 US troops — perhaps even 1,200 — would be sent to participate in the exercise instead of the original 5,000. In addition, sources in both Jerusalem and Washington told Time that it was probable that only one Aegis Ballistic Missile Defense warship — instead of two — would be sent to Israel.

The Patriot anti-missile systems set to be dispatched to Israel would reportedly arrive as planned, but not the crews to operate them.

Following the report, sources in Washington immediately denied that the move conveyed mistrust. “Austere Challenge 12 remains the largest-ever ballistic missile defense exercise between our nations and a significant increase from the previous event in 2009,” Air Force Lieutenant Colonel Jack Miller, a Pentagon spokesman, told Reuters later on Friday.

“The exercise has not changed in scope and will include the same types of systems as planned. All deployed systems will be fully operational with associated operators,” Miller said.

Commander Wendy L. Snyder of the US Army, meanwhile, was quoted by Time as saying that “throughout all the planning and coordination, we’ve been lock-step with the Israel Defense Force (IDF) and will continue to do so.”

However, sources in the Israeli defense establishment were reportedly unconvinced, with one senior military official telling Time, “Basically what the Americans are saying is, ‘We don’t trust you.’”

Other sources in the Israeli defense establishment on Saturday denied the accuracy of the Time report saying Israel never received notification from the Americans of the reduction. As far as the IDF is concerned, they added, the drill will proceed as planned.

The drill was planned to simulate missiles being fired at Israel from Iran and Syria simultaneously, with potentially dozens, if not hundreds, of rockets mid-air at the same time. Israel was to test its upgraded Arrow 2 defense system, while the US was to deploy the Aegis Ballistic Missile Defense System and PAC-3 Patriot air defense platforms.