Pushing back hard, President Barack Obama forcefully defended the temporary agreement to freeze Irans 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 its 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 Tehrans disputed nuclear program and allow for more intrusive international monitoring of Irans facilities.

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.

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, Ive done what Ive 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.

On the positive side, Michael Desch, a political science professor at the University of Notre Dame, compared Obamas diplomatic overtures to Secretary of State Henry Kissingers 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.