Israeli Prime Minister Benjamin Netanyahu warned on Tuesday that a nuclear-armed Iran would be "a thousand times more dangerous and more destructive" than the Islamic State group, his office said.

"As horrific as ISIS is, once Iran, the preeminent terrorist state of our time, acquires nuclear weapons, it will be a hundred times more dangerous, a thousand times more dangerous and more destructive than ISIS," Netanyahu said, referring to IS.

His remarks came as political and technical experts representing Iran and world powers were to convene in Vienna ahead of a June 30 deadline for a deal over Tehran's nuclear programme.

"As we are meeting, the P5+1 talks are reconvening, and I'm afraid they're rushing to what I consider is a very bad deal," Netanyahu told US Senator Bill Cassidy, in remarks relayed by the Israeli premier's office.

"I see no reason to rush to a deal and certainly not a bad deal that paves Iran's path to the bomb, but also fills Iran's coffers with tens of billions of dollars to pursue its aggression throughout the Middle East and around Israel's borders," he said.

Netanyahu has been a fierce critic of the looming deal between Iran and world powers comprising the United States, Britain, China, France, Russia and Germany.

The accord would finalise an April 2 deal preventing Tehran from developing nuclear weapons in exchange for an easing of crippling economic sanctions.

"We shouldn't give Iran a path to nuclear weapons and billions of dollars to pursue aggression because of ISIS," Netanyahu said of the group, which both the US and Iran see as a threat.

"ISIS should be fought; Iran should be stopped."