NPR.org, December 4, 2007 · The controversy over Iran's nuclear program is complicated by the country's decision to resume efforts to enrich uranium — defying the United Nations despite saying it had stopped researching nuclear weapons.

Iranian officials said they wanted the enriched radioactive material as fuel for peaceful nuclear reactors. When President Bush and other administration officials accused Iran of seeking to develop a nuclear bomb, they often referred to Iran's uranium-enrichment program as proof.

Here's a timeline highlighting what was said and known about the program since early 2003:

February 2003: Inspectors from the International Atomic Energy Agency (IAEA), the United Nations nuclear watchdog agency, find evidence that Iran has secretly begun enriching uranium.

May 2003: Iranian President Mohammed Khatami offers to talk to the United States about the countries' differences. But the Bush administration rejects the offer. In part because of this refusal, the Europeans act on their own to negotiate with the Iranians while trying to persuade the Bush administration to join the negotiation process.

October 2003: The EU 3 — France, Britain and Germany — reach an initial understanding with Iran to suspend nuclear enrichment. The Bush administration refuses to support this, insisting suspension of nuclear enrichment is not enough. The Bush administration insists that before it will enter into any negotiations with the Iranians, Iran must commit to abandoning enrichment altogether.

November 2003: The IAEA announces that Iran has been violating its safeguards agreement under the Nuclear Non-Proliferation Treaty. It accuses Tehran of failing to report that it was handling nuclear material and building facilities to process it. It says Iranian officials hid key parts of their nuclear program for nearly 20 years. The latest National Intelligence Estimate now says it believes "with high confidence" that the fall of 2003 was about the time Iran shut down a secret nuclear weapons program.

December 2003: After talks with the European Union, Tehran agrees to allow IAEA inspectors to expand their operations in Iran, by questioning its scientists and officials, reviewing documents and conducting further examinations of some of its nuclear research and development facilities.

November 2004: Iran promises negotiators from the EU that it will suspend all its activities for processing nuclear fuel. Although Iran continues to deny that its activities have any military purpose, President Bush calls it a "nuclear weapons program" and chides Iran's leaders for suspending it, rather than ending it entirely. "Our position is that they ought to terminate their nuclear weapons program," Bush says.

February 2005: President Bush accuses Iran of being "the world's primary state sponsor of terror, pursuing nuclear weapons, while depriving its people of the freedom they seek and deserve."

June 2005: Secretary of State Condoleezza Rice says the United States will not support a third term for Mohammed ElBaradei as head of the IAEA unless he takes a harder line against Iran's nuclear program.

April 2006: Iranian President Mahmoud Ahmadinejad says Iranian scientists have successfully enriched uranium to the 3.5 percent level, pure enough to run a nuclear reactor. He says, "I am officially announcing that Iran has joined the group of those countries which have nuclear technology." Uranium for a nuclear bomb would require around 90 percent enrichment.

July 2006: The United Nations Security Council passes a resolution demanding that Iran suspend its nuclear enrichment activities or face international sanctions.

December 2006: The U.N. Security Council unanimously imposes sanctions on Iran for failure to halt its uranium enrichment program. It bans U.N. member states from providing Iran with equipment or technology that could be used in its nuclear program.

January 2007: IAEA head Mohammed ElBaradei calls for a "timeout" on the issue of Iran's nuclear program, saying the United Nations should suspend sanctions against Iran if Iran will freeze its nuclear program. He tells CNN, "The key to the Iranian issue is a direct engagement between Iran and the U.S., similar to North Korea."

Spring 2007: A National Intelligence Estimate on Iran was expected to be delivered to Congress during this period, but is repeatedly postponed as intelligence agencies re-assess information about Iran's nuclear program.

August 2007: President Bush says, "Iran's active pursuit of technology that could lead to nuclear weapons threatens to put a region already known for instability and violence under the shadow of a nuclear holocaust." The latest National Intelligence Estimate says, "we assess with moderate confidence Tehran had not restarted its nuclear weapons program as of mid-2007."

September 2007: U.S. intelligence officials, including CIA Director Michael Hayden, begin a reassessment of their information on Iran, according to unnamed officials quoted in the New York Times. The newspaper says White House officials knew at the time that the intelligence agencies were reviewing their conclusions, but did not know until later that those conclusions were drastically being changed.

October 2007: President Bush says, "we got a leader in Iran who has announced that he wants to destroy Israel. So I've told people that if you're interested in avoiding World War III, it seems like you ought to be interested in preventing them from having the knowledge necessary to make a nuclear weapon."

November 2007: A final draft of the National Intelligence Estimate is presented to President Bush and Vice President Dick Cheney. It concludes that Iran stopped its weapons program in late 2003 and since then has shown no signs of resuming it.

December 2007: A day after the NIE is made public, President Bush says he was first told by Director of Intelligence Michael McConnell in August that there was new intelligence about Iran's nuclear program, but that he wasn't told what that new intelligence was at the time. President Bush, in a press conference, says he still regards Iran as "dangerous." He asks reporters, "What's to say they couldn't start another covert nuclear weapons program?"