Amid rising concerns about the prospect of the Iranian government making a nuclear weapon, President Obama today assured Israeli Prime Minister Benjamin Netanyahu that "the United States will always have Israel's back when it comes to Israel's security."

In contrast to the tense Oval Office meeting of last May, when the president and prime minister were more focused on the stalled Israel-Palestinian peace process Obama and Netanyahu today sounded united, though behind the scenes they are working through some contentious issues on how to best discourage Iran from continuing with any plans to manufacture a nuclear weapon.

Echoing remarks he delivered Sunday to the influential American Israel Public Affairs Committee, Obama argued that diplomacy is the best way to resolve the issue but that all options, including military action, are on the table.

"We will continue to tighten pressure when it comes to sanctions, I reserve all options. And my policy here is not going to be one of containment. My policy is prevention of Iran obtaining nuclear weapons," Obama said. "When I say all options are at the table, I mean it."

The U.S. and Israel differ on timelines and red lines. Obama believes there is "still a window" for diplomatic and economic pressures to work.

"Both the prime minister and I prefer to resolve this diplomatically.  We understand the costs of any military action, and I want to assure both the American people and the Israeli people that we are in constant and close consultation," Obama said.

Obama's continued call for diplomacy comes as the Israelis have asked for the White House to more starkly threaten military action against Iran if it continues to violate its international agreements to refrain from building a nuclear weapon. While the U.S. has called for Iran to not manufacture a weapon, Israel wants to go even further and prevent Iran from having the capability to build a weapon, and has asked the U.S. to push Iran to end its program of enriching uranium.

The president today did not go that far, but he broke from some in his own party by emphasizing his belief that the threat from Iran is real. He said it is "profoundly in the United States' interest as well to prevent Iran from obtaining a nuclear weapon" and added that "we do not want to see a nuclear arms race in one of the most volatile regions in the world.  We do not want the possibility of a nuclear weapon falling into the hands of terrorists."

In his remarks Netanyahu emphasized unity, saying that Israel and America stand together, complete with a Beatles-esque flourish that "we are you, and you are us; we're together."

The prime minister underscored that Israel is a sovereign nation with the right to defend itself. "My supreme responsibility as prime minister of Israel is to ensure that Israel remains the master of its fate," Netanyahu said.

- Jake Tapper and Mary Bruce