In an interview with Israel's Channel 2 on Thursday, ahead of his visit next week, Obama said the United States estimated it would take Iran "over a year or so" to develop a nuclear weapon, once Tehran decided to pursue one.
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He also acknowledged the differences he has had with Israeli Prime Minister Benjamin Netanyahu, but said the foundation of bilateral ties was strong, as was his commitment to Israel's security.
Obama said he and Netanyahu shared a "terrific, business-like relationship", and a number of times referred to the Israeli leader as Bibi, his popular childhood nickname.
Regarding the long-stalled peace process with the Palestinians, Obama spoke somewhat vaguely, saying he was coming to listen during meetings he would hold with Netanyahu and Palestinian President Mahmoud Abbas.
Obama's first presidential visit to Israel comes at the onset of spring - the "red line" previously set by Netanyahu for attacking Iran's nuclear sites.
Iran denies it is seeking a bomb and says its nuclear program is solely for peaceful purposes.
"We think that it would take over a year or so for Iran to actually develop a nuclear weapon, but obviously we don't want to cut it too close," Obama said.
Asked if he would order an attack on Iran should diplomacy fail, Obama said: "When I say that all options are on the table, all options are on the table. The United States obviously has significant capabilities but our goal here is to make sure that Iran does not possess a nuclear weapon that could threaten Israel or could trigger an arms race in the region."
'My goal is to listen'
During the visit, Obama faces the challenge of overcoming Israeli suspicions that have lingered since his early days in office when he pressed Netanyahu for a freeze on settlement expansion and launched a short-lived outreach to Tehran, Israel's arch-foe.
Netanyahu, victorious in a January election, only clinched a coalition deal on Thursday, and Obama said any breakthrough in peace negotiations with the Palestinians would be unlikely until the Israeli government stabilized.
"My goal on this trip is to listen," he said.
Obama stopped short of calling for a freeze in settlement building in the occupied West Bank, but suggested a change in Israel's policy would empower moderate Palestinian leaders.
He said "it's a matter of both parties coming together and recognizing that their futures in some ways are going to inextricably linked and that Israel will be safer, more secure, more prosperous if the issue can be resolved".
"Obviously Israel can't resolve it by itself, but it can't stop trying."
In a direct appeal to the Israeli people, Obama said he regretted that he would not have an opportunity to walk the streets and hear what average folks have to say.
"Sometimes I have this fantasy that I can put on a disguise, wear a fake moustache, and I could wander through Tel Aviv, go to a bar, and, you know, have a conversation there," he said.
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