US Republican candidate Mitt Romney has said that "any and all measures" must be used to keep Iran from developing a nuclear weapon.
In Jerusalem, Romney voiced strong support for the alliance between the US and Israel and seemed to suggest that President Barack Obama had let the relationship flounder.
The former Massachusetts governor was in Jerusalem on the second leg of a trip to strengthen his foreign policy credentials.
The presidential hopeful was greeted warmly earlier by Israeli Prime Minister Benjamin Netanyahu, an old friend of his, who has at times had a strained relationship with Obama.
Netanyahu issued his customary call for stronger measures behind the sanctions to prevent Iran from developing an atomic bomb.
Israel says would be a threat to its existence. Iran says its nuclear program is for peaceful purposes.
Israel, widely assumed to be the Middle East's only nuclear-armed state, has warned it is only a matter of time before Iran's nuclear programme achieves a "zone of immunity" in which uranium enrichment facilities buried deep underground will be invulnerable to bombing.
Though Washington has been pressing Israel not to launch a solo strike on Iran, Obama has not ruled out military action if diplomacy fails to curb Iran's nuclear drive.
