"As president of the United States, I don't bluff," Obama warned Iran in a magazine interview published on Friday, three days before he will host Israeli Prime Minister Benjamin Netanyahu in Washington.
With the meeting expected to be dominated by stark differences over what Washington fears could be an Israeli attack on Tehran's nuclear sites, Netanyahu said he wanted to preserve the "freedom of action of the State of Israel in the face of threats to wipe us off the map."
Monday's talks are shaping up as the most consequential encounter of U.S. and Israeli leaders in years, with tensions further magnified by Republican presidential candidates slamming Obama over his Middle East policy.
Further complicating the talks is a trust deficit between the two men, who have had a rocky relationship.
There is mounting speculation that Israel, which fears that time is running out to stop Iran's nuclear advance, could act militarily on its own in 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, while the U.S. president wants to convince Israel to hold off on any unilateral strike and give sanctions and diplomacy more time to work.
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 said in an interview with the Atlantic magazine.
Obama repeated the U.S. refrain that "all options are on the table" but spoke in his most direct terms yet of a possible U.S. military response if sanctions and diplomacy fail to curb Tehran's nuclear ambitions.