(AP) -- Capping a week of difficult and often contentious negotiations, the United States, Iran and five other world powers said Thursday they had agreed on an outline of limits on Iran's nuclear program that would prevent it from developing nuclear weapons in exchange for sanctions relief. The announcement, following talks that burst through a March 31 deadline amid deep uncertainty about the outcome, begins another three months of more detailed negotiations during which the nations will try to reach a comprehensive final accord to achieve the limits.

The United States, Iran and other countries involved in the effort each hailed the framework, which reached by weary but upbeat diplomats after seven days of often sleepless nights in Switzerland. Those involved have spent 18 months in broader negotiations that had to be extended twice due to an inability to bridge wide gaps in positions since they reached an interim accord in November 2013. The November deal itself was the product of more than a year of secret negotiations between the Obama administration and Iran, a country the U.S. still accuses of being the world's leading state sponsor of terrorism.

Speaking at the White House, President Barack Obama called it a "good deal" that would address concerns about Iran's nuclear ambitions. But critics of the emerging deal, including Israel, reacted with skepticism, saying the parameters laid out do not effectively curb Iran's ability to produce a nuclear weapon, deny it the technology to do so, or mandate the intrusive inspections needed to verify Iranian compliance.

"I am convinced that if this framework leads to a final comprehensive deal, it will make our country, our allies and our world safer," Obama declared. "It is a good deal, a deal that meets our core objectives."

Obama sought to stave off criticism, notably from Congress where there is strong opposition to the negotiations by promising to fully brief lawmakers on all the details.

Appearing in the Rose Garden, he said the issues at stake are "bigger than politics." ''These are matters of war and peace, and they should be evaluated based on the facts," he said.

He also maintained that "if there is backsliding on the part of the Iranians, if the verification and inspection mechanisms don't meet the specifications of our nuclear and security experts, there will be no deal."

Several of the agreed-upon restrictions apply to Iran's enrichment of uranium, a core concern because the material can be used in a nuclear warhead and the conversion of a heavy-water reactor that could produce weapons-grade plutonium, another path to an atomic bomb. Others will prevent any work with uranium at a previously secret facility buried deep underground and the confinement of all uranium activity to one facility that is already being monitored. Many of limits will be in place for 10 years, others for 15 and 20 and some that covered by international accords Iran is already party to will be in place for longer.

In return, economic and financial sanctions related to Iran's nuclear programs are to be rolled back by the U.S., the United Nations and European Union after the U.N. nuclear agency confirms Iran's compliance.

In the Swiss city of Lausanne where the framework was presented, European Union foreign policy chief Federica Mogherini and Iranian Foreign Minister Mohammad Javad Zarif read out a joint statement, hailing what they called a "decisive step" after more than a decade of work. U.S. Secretary of State John Kerry and the top diplomats of Britain, France and Germany took the stage behind them.

"We have taken a major step, but are still some way away from where we want to be," Zarif told reporters after the statement was read, calling the agreed-upon understandings a "win-win outcome." He voiced hope that a final agreement might pave the way for a broader easing of suspicion between the U.S. and Iran, which haven't had diplomatic relations since the 1979 overthrow of the shah and subsequent U.S. Embassy hostage crisis in Tehran.

Zarif said the agreement would show "our program is exclusively peaceful, has always been and always will remain exclusively peaceful," while not hindering the country's pursuit of atomic energy for civilian purposes. "We will continue enriching," he said. "We will continue research and development." He said the heavy water reactor would be "modernized."

Such comments are likely to fuel criticism.

Kerry declined to comment on any possible implications of the agreement for a rapprochement between the United States and Iran. And, speaking after Zarif, he lashed out at critics of the emerging agreement who have demanded that Iran halt all uranium enrichment and completely close the underground facility among other more stringent measures.

"Simply demanding that Iran capitulate makes a nice sound bite, but it is not a policy, it is not a realistic plan," Kerry said.

The final breakthrough came a day after a flurry of overnight sessions between Kerry and Zarif, and meetings involving the six powers at a luxury hotel in Lausanne.

As late as Thursday afternoon, it appeared that an agreement was far away with the U.S. and Iran deeply split on the content of the statement to be delivered. The U.S. had wanted a statement of general principles to be accompanied by additional documents detailing specific measures that must be taken. Iran adamantly opposed that, demanding that only a vague statement be presented. In an apparent compromise, some details were included in the general statement and a more detailed position paper was issued by the White House and State Department afterward.

Israeli leaders, deeply concerned about Iran's intentions, were much less positive.

Prime Minister Benjamin Netanyahu said a final agreement "must significantly roll back Iran's nuclear capabilities and stop its terrorism and aggression."

Obama and Kerry both said the comprehensive agreement would make Israel and Gulf Arab allies safer and the president said he would be calling Netanyahu to explain his thinking.

"If, in fact, Prime Minister Netanyahu is looking for the most effective way to ensure Iran doesn't get a nuclear weapon, this is the best option," Obama said.

"We have vigorously reaffirmed our enduring commitment to their security."

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AP writers Julie Pace and Bradley Klapper contributed to this report from Washington.