US President Barack Obama declared an interim nuclear deal with Iran an "important first step" that cuts off the Islamic republic's most likely path toward a bomb.
"These are substantial limitations which will help prevent Iran from building a nuclear weapon," Obama said during remarks from the White House late Saturday.
The president spoke shortly after the US and five international partners agreed to a short-term deal with Iran that is aimed at making the way for a broader agreement to curb Tehran's disputed nuclear program. Under the terms of the deal, Iran agreed to halt progress on key elements of its nuclear program in exchange for modest relief from U.S. economic sanctions.
Obama pledged to hold off from imposing new sanctions during the terms of the six-month agreement, a position likely to anger some in Congress who have been pushing for even tougher penalties against Iran.
"If Iran does not fully meet its commitments during this six-month phase, we will turn off the relief and ratchet up the pressure," he said. Some in Congress remained wary about the deal.
Republican Sen. Marco Rubio, a potential presidential candidate in 2016, pledged to work with others in the Senate to increase the economic pressure on Iran until it "completely abandons" its capability to enrich and reprocess the uranium needed to make weapons.
"This agreement makes a nuclear Iran more, not less, likely," Rubio said in a statement.
Obama came into office promising to talk to Iran without preconditions. The US and Iran broke off diplomatic ties in 1979 after the Islamic revolution and the storming of the U.S. Embassy in Tehran, where dozens of Americans were held hostage for more than a year.
The June election of Iranian President Hassan Rouhani, a more moderate-sounding cleric, helped pave the way for a thaw in diplomatic relations with the U.S., a historic phone call between the two presidents and this latest round of nuclear negotiations.
Obama's outreach to Iran has worried Israel and Persian Gulf nations, which fear Iran is using the negotiations as a delay tactic while it continues to pursue a nuclear weapon.
The president said those nations "have good reason to be skeptical of Iran's intentions." But he said "only diplomacy can bring about a durable solution to the challenge posed by Iran's nuclear program."
Rabbi Steve Gutow, president of the Jewish Council for Public Affairs, said that while "Iran has done little to deserve our trust," the agreement "has the potential to serve as a valuable stepping stone to a final agreement that can serve the long-term security interests of the United States, Israel, the Middle East and the entire international community."
Gutow said any final agreement must not leave Iran able to continue its drive for nuclear weapons capability, or able to easily restart its program at any point in the future.
"The menace of a nuclear-armed Iran needs to be eliminated once and for all," Gutow said.