Pushing back hard, President Barack Obama forcefully defended the temporary agreement to freeze Iran’s disputed nuclear program on Monday, declaring that the United States “cannot close the door on diplomacy.”

The president’s remarks followed skepticism of the historic accord expressed by some U.S. allies abroad as well as by members of Congress at home, including fellow Democrats. Israeli Prime Minister Benjamin Netanyahu, one of the fiercest opponents of the six-month deal, called it a “historic mistake” and announced he would be dispatching a top envoy to Washington to try to toughen the final agreement negotiators will soon begin hammering out.

Obama, without naming names, swiped at those who have questioned the wisdom of engaging with Iran.

“Tough talk and bluster may be the easy thing to do politically, but it’s not the right thing to do for our security,” he said during an event in San Francisco.

The weekend agreement between Iran and six world powers — the U.S., Britain, France, Russia, China and Germany — is to temporarily halt parts of Tehran’s disputed nuclear program and allow for more intrusive international monitoring. In exchange, Iran gains some modest relief from stiff economic sanctions and a pledge from Obama that no new penalties will be levied during the six months.

Despite the fanfare surrounding the agreement, administration officials say key technical details on the inspections and sanctions relief must still be worked out before it formally takes effect. Those talks will tackle the toughest issues that have long divided Iran and the West, including whether Tehran will be allowed to enrich uranium at a low level.

Iran insists it has a right to enrich uranium for peaceful purposes, and many nuclear analysts say a final deal will almost certainly leave Iran with some right to enrich. However, that’s sure to spark more discord with Israel and many lawmakers who insist Tehran be stripped of all enrichment capabilities. British Foreign Secretary William Hague said he expects the deal to be fully implemented by the end of January.

European Union officials say their sanctions could be eased as soon as December. Those restrictions affect numerous areas including trade in petrochemicals, gold and other precious metals, financial transfers to purchase food and medicine, and the ability of third countries to use EU-based firms to insure shipments of Iranian oil again.

The groundwork for the accord was laid during four clandestine meetings between U.S. and Iranian officials throughout the summer and fall. An earlier meeting took place in March, before Iranians elected President Hassan Rouhani, a cleric who has taken more moderate public stances than his predecessor. Details of the secret talks were confirmed to The Associated Press by three senior administration officials.

The U.S. and its allies contend Iran is seeking to produce a nuclear bomb — of particular concern to Israel, which fears an attack — while Tehran insists it is merely pursuing a peaceful nuclear program for energy and medical purposes.

Even with the criticism, for Obama the sudden shift to foreign policy presents an opportunity to steady his flailing second term and take some attention off the domestic troubles that have plagued the White House in recent weeks, especially the rollout of his signature health care law. Perhaps with his presidential standing — and the strength of the rest of his term — in mind, he made sure on Monday to draw a connection between the nuclear pact and his long-declared willingness to negotiate directly with Iran.

“When I first ran for president, I said it was time for a new era of American leadership in the world, one that turned the page on a decade of war and began a new era of engagement with the world,” he said. “As president and as commander in chief, I’ve done what I’ve said.”

The temporary accord is historic in its own right, marking the most substantial agreement between Iran and the West in more than three decades. The consequences of a permanent deal could be far more significant, lowering the prospects of a nuclear arms race in the volatile Middle East and perhaps opening the door to wider relations between the U.S. and Iran, which broke off diplomatic ties following the 1979 Islamic revolution.

However, Obama and his advisers know the nuclear negotiations are rife with risk. If he has miscalculated Iran’s intentions, it will vindicate critics who say his willingness to negotiate with Tehran is naive and could inadvertently hasten the Islamic republic’s march toward a nuclear weapon. Obama also runs the risk of exacerbating tensions with key Middle Eastern allies, as well as members of Congress who want to deepen, not ease, economic penalties on Iran.

Despite Obama’s assurances that no new sanctions will be levied on Iran while the interim agreement is in effect, some lawmakers want to push ahead with additional penalties. A new sanctions bill has already passed the House, and if it passes the Senate, Obama could have to wield his veto power in order to keep his promise to Tehran.

Even some members of Obama’s own party say they’re wary of the deal struck in Geneva.

“I am disappointed by the terms of the agreement between Iran and the P5+1 nations because it does not seem proportional,” said Sen. Chuck Schumer, D-N.Y., a close ally of the White House. “Iran simply freezes its nuclear capabilities while we reduce the sanctions.”

The Senate’s Democratic majority leader, Harry Reid, was noncommittal on the subject of sanctions on Monday. On NPR’s Diane Rehm Show, he said that when lawmakers return from their Thanksgiving break, “we will take a look at this to see if we need stronger sanctions … and if we need work on this, if we need stronger sanctions I am sure we will do that.”

Some lawmakers are also concerned about concessions the world powers made to Iran on its planned heavy water reactor in Arak, southwest of Tehran. Two congressional aides said that under the terms of the agreement, international monitors will not being able to watch live feeds of any activity at Arak and will instead retrieve a recording from the preceding day during each daily inspection.

The aides were not authorized to provide details of the agreement and demanded anonymity.

On the positive side, Michael Desch, a political science professor at the University of Notre Dame, compared Obama’s diplomatic overtures to Secretary of State Henry Kissinger’s secret outreach to China in the 1970s, which paved the way for the historic opening of U.S. relations with the Asian nation.

“Then, as now, critics complained that the U.S. was in danger of being hoodwinked by a radical and violent regime that was playing us for a sucker,” Desch said. “An opening to Iran could potentially not only contain its nuclear program but set the stage for broader changes there as well.”

(AP)