"This is an important step forward to start with, but much more needs to be done," International Atomic Energy Agency Director-General Yukiya Amano said during a news conference after the signing.
"Under the Framework, Iran and the IAEA will cooperate further with respect to verification activities to be undertaken by the IAEA to resolve all present and past issues" Amano said
Iran's cooperation will include providing the IAEA with timely information about its nuclear facilities and on implementing transparency measures, the United Nations said in a release. The IAEA agreed to consider Iran's security concerns.
Iran's nuclear program -- which its leaders say is for peaceful purposes, but other countries contend it is to develop nuclear weapons -- has been a matter of international concern since the discovery in 2003 that the country had concealed its nuclear activities for 18 years, breaching its obligations under the Nuclear Non-Proliferation Treaty, the United Nations said in a release.
The Joint Statement on a Framework for Cooperation, signed by Amano and Iranian Vice President Ali Akbar Salehi, includes an appendix listing measures to be taken as a first step by Iran within three months.
The measures include providing mutually agreed-upon relevant information and access to the Gchine mine and the Heavy Water Production Plant; providing information on all new research reactors; providing information on the identification of 16 sites designated for nuclear power plant construction and clarification on the announcements made by Iran concerning more enrichment facilities and laser enrichment technology.
Amano said any unresolved issues not in the list will be addressed later.
Meanwhile, the White House will make "absolutely certain" Iran "never has a nuclear weapon," U.S. Secretary of State John Kerry said before returning to Washington Monday.
He was returning to Washington to appear before skeptical lawmakers on Capitol Hill to defend a proposed deal that would temporarily freeze some of Iran's nuclear programs in exchange for a partial easing of Western sanctions.
Congress is threatening to push through additional economic sanctions against Tehran, a move diplomats say would likely complicate the talks.
The additional sanctions, which would end if an acceptable deal were reached, would be "insurance for the United States to make sure that Iran actually complies with an agreement that we would want to see," Sen. Robert Menendez, D-N.J. -- a member of the Banking Committee, which would vote first on the bill -- told ABC's "This Week" Sunday.
The possible deal with Iran, which did not materialize during the weekend despite diplomatic statements it was close, would be a first phase, lasting six months, followed by a bigger deal, Kerry told NBC's "Meet the Press."
The goal is to freeze part of Iran's nuclear program during the first phase to create breathing room for the comprehensive agreement between Iran and the five permanent U.N. Security Council members -- the United States, Russia, China, Britain and France -- and Germany, he said. The world powers group is often known as the P5-plus 1.
Other senior U.S. diplomats went to Israel and the Persian Gulf to try to win over skeptical allies and show the delay could ultimately lead to a better deal with Tehran, officials said.
Saudi Arabia and the other Gulf states see Iran as a regional threat and agree with Israel, in a rare coalition, that Tehran should have no ability to enrich uranium.
"We are not blind, and I don't think we're stupid," Kerry told the NBC program.
"I think we have a pretty strong sense of how to measure whether or not we are acting in the interests in our country, and of the globe, and particularly of our allies, like Israel and Gulf states and others in the region.
"We are absolutely determined that this would be a good deal," Kerry said, "or there'll be no deal."
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