WASHINGTON: US Secretary of State John Kerry said on Friday it would be a huge mistake if Israel decided to take unilateral military action against Iran over its nuclear program in the future.

Kerry was asked in an NBC "Today" show interview if the nuclear deal reached last week would make it more likely that Israel might attempt a military or cyber attack on Tehran.

"That'd be an enormous mistake, a huge mistake with grave consequences for Israel and for the region, and I don't think it's necessary," Kerry said.

He warned later on Friday that if Congress failed to approve the deal agreed last week between world powers and Iran to curb Iran's nuclear programme then Israel could be worse off. Congress has until Sept. 17 to approve or reject the agreement.

"I fear that what could happen is if Congress were to overturn it, our friends in Israel could actually wind up being more isolated and more blamed," Kerry told the Council on Foreign Relations think tank in New York.

"We would lose Europe and China and Russia with respect to whatever military action we might have to take because we will have turned our backs on a very legitimate program that allows us to put their program to the test over these next years," he said.

Under the deal agreed in Vienna, U.S., EU and U.N. sanctions will be lifted in exchange for long-term curbs on Iran's nuclear program that the West suspected was aimed at creating an atomic bomb, but which Tehran says is peaceful.