A nuclear-armed Iran would be a "game-changer for the region," allowing the Islamic republic to meddle through extremist proxies, intervene in Iraq and threaten oil supplies, the Democrat told about 250 voters at a meeting here.

"My job as president is to make sure we are tightening the screws on Iran diplomatically... to get sanctions in place so that Iran starts making a different calculation," the Illinois senator said.

"And we've got to do that before Israel feels like its back is against the wall."