US President Barack Obama issued his most direct threat yet of US military action against Iran if it builds a nuclear weapon, but in a message to Israel's leader ahead of White House talks he also cautioned against a pre-emptive Israeli strike.
"As president of the United States, I don't bluff," Obama warned Iran in a magazine interview published on Friday, three days before a crucial meeting with Israeli Prime Minister Benjamin Netanyahu.
With the talks expected to be dominated by stark differences over what Washington fears could be an Israeli rush to attack Tehran's nuclear sites, Obama's remarks appeared intended to offer some degree of the assurances that Netanyahu has demanded for greater public resolve against Iran.
Netanyahu, on a visit to Canada on Friday, sought to avoid widening the rift with Obama but insisted on the right to preserve "freedom of action of Israel in the face of threats to wipe us off the map."
Monday's meeting is shaping up as the most consequential encounter of US and Israeli leaders in years. Tensions have been magnified in a US election year, with Republican presidential contenders slamming Obama as too soft on Iran and too hard on Israel, a close ally.
Further complicating the situation is a trust deficit between Obama and Netanyahu, who have had an often strained relationship. There is mounting speculation that Israel, which fears that time is running out to stop Iran as it buries nuclear facilities further underground, could act militarily on its own in the coming months unless it receives stronger reassurances from Washington.
Netanyahu is trying to convince Obama to more forcefully define the nuclear threshold that Iran must not cross and the consequences it would face if it did so. The US president, who told the Atlantic that he "has Israel's back," wants to convince the right-wing Israeli leader to hold off on any unilateral strike and give sanctions and diplomacy more time to work. Iran remains defiant but denies it is trying to develop nuclear weapons.
Both leaders talked tough ahead of their meeting.
"I think both the Iranian and the Israeli governments recognize that when the United States says it is unacceptable for Iran to have a nuclear weapon, we mean what we say," Obama told the Atlantic magazine.