(CNN) -- Iran may be working on secretly developing a nuclear warhead for a missile, the head of the United Nations' nuclear watchdog agency said Thursday in a draft report.

It's the first time that the the International Atomic Energy Agency has issued such a strong warning about current Iranian nuclear activities.

The statement is in an IAEA draft report obtained by CNN. The report, dated Thursday, has not yet been approved by the board of governors of the IAEA.

It is the first report by the agency's new director general, Yukiya Amano, who replaced Mohamed ElBaradei at the end of last year.

White House Press Secretary Robert Gibbs, speaking to reporters aboard Air Force One, said the report "demonstrates for the world again the obligations [Iran's government is] failing to live up to."

Administration officials have "always said that if Iran failed to live up to those international obligations, that there would be consequences," he said.

The paper lists a catalog of ways in which the Islamic state is allegedly defying U.N. orders about its nuclear program.

The United States and its allies fear that Iran aims to develop the capacity to build a nuclear bomb. Iran denies it, saying its nuclear program is designed for civilian energy and medical use.

The agency previously expressed concerns about Iran's past nuclear activities, but Thursday's draft report seems to be the first time it has warned about current Iranian activities.

There was no immediate reaction from Iran's government.

The report also noted that Iran began enriching uranium to a level at which it can sustain a nuclear reaction before IAEA inspectors arrived to monitor the process and in defiance of a specific request that it not do so.

The IAEA asked Iran earlier this month not to boost uranium enrichment to 20 percent "before the necessary additional safeguard procedures were in place," it said in the report.

When inspectors arrived at the Natanz nuclear plant the next day, February 10, "they were informed that Iran had already begun to feed the low enriched" uranium into the enrichment machinery the previous evening.

Iran needs to put more measures in place at Natanz so the IAEA can ensure it is not concealing nuclear material, the agency said in its report.

The IAEA also reported on the construction of a new nuclear plant, the Fordow plant near Qom.

No centrifuges have been introduced into the plant as of Tuesday, the report said. Centrifuges are machines that spin at high speed, a part of the enrichment process.

Iran shocked the world in September by revealing it was working on the Fordow plant, which previously had been secret.

In Washington, Assistant Secretary of State P.J. Crowley noted that the report is the first one the IAEA has produced since the discovery of the secret nuclear facility at Qom.

"There is no explanation for that facility that is consistent with the needs of a civilian nuclear program. And it characterizes the way in which Iran has conducted its ... relations with the IAEA and its failure to satisfactorily explain, you know, what its activities and ambitions are in the nuclear sphere," he said.

Crowley said the conclusions of the report "are consistent" with arguments Secretary of State Hillary Clinton made in the Middle East during her visit this week.

"We have ongoing concerns about Iran's activities," Crowley said Thursday at the regular daily briefing at the State Department. "We cannot explain why it refuses to come to the table and engage constructively to answer the questions that have been raised, and you have to draw some conclusions from that."

On Sunday, Clinton, speaking at the World Islamic Forum in Doha, Qatar, called for tougher actions against Iran after its announcement that it is stepping up production of highly enriched uranium.

"Iran has consistently failed to live up to its responsibilities," Clinton said Sunday. "It has refused to demonstrate to the international community that its nuclear program is entirely peaceful."

In January, the Islamic republic refused to let international inspectors take samples of what it claimed was heavy water, the IAEA said in its report Thursday. Heavy water can be a key component in making plutonium, according to the Federation of American Scientists.

The U.N. Security Council ordered Iran to suspend any work on heavy-water projects in 2006.

The report highlighted concerns about rising tensions in the Middle East, particularly between Iran and Israel. Israel has often been the object of rhetoric by Iranian President Mahmoud Ahmadinejad, who has said the Jewish state "must be wiped off the map" politically. The United States has had to assure Israel that its interests will be protected to keep its military on the sidelines.

Former IAEA weapons inspector David Albright said Thursday that Iran's behavior "has to make you worry more about a [potential] conflict."

Iran appears to be "pushing" for concessions from the United States and other Western powers, he said.

"They're pushing on things that make them look like they're going for nuclear weapons, and that's risky. If they go much further, they may bring an attack on themselves by Israel. Iran needs to be a little more careful about its actions," Albright said.

But Michael Levi, a nuclear proliferation analyst at the Council on Foreign Relations, said in an interview that "in a sense, we should be pleased by this."

"Having such a clear statement from an international body can only help develop a robust international response," Levi said.

Levi said he doesn't think "there's anything in here that Israel did not already believe."

"It shouldn't change Israel's calculus. To the extent that it can spur robust nonmilitary response, that makes military action potentially less necessary and therefore less likely," Levi said.

Both Albright and Levi argued that the best response from the Obama administration would be to use the report to help build momentum for stronger international sanctions and diplomatic pressure.

"The good news is ... the nuclear program is running into some technical problems, which are slowing down their ability to produce enriched uranium," a senior administration official told CNN Thursday. "The bad news is that they seem to be increasing their lack of cooperation with the IAEA."

Absent increased international pressure on Iran, "this program is heading more and more in the direction of seeking a weapons capability," the senior official said, adding, "I think there's less and less credibility to the Iranian statement that their program is peaceful and much stronger international recognition that we're facing a country that's seeking a nuclear weapons capability."

On Tuesday, Ahmadinejad warned the United States and other nations not to impose tougher sanctions in reaction to Iran's nuclear ambitions.

"It's high time for some people to open their eyes and adapt themselves to real changes that are under way," he said at a news conference in Tehran.

Asked specifically about the threat of tougher sanctions, Ahmadinejad said, "We prefer that they move in the spirit of cooperation. It won't put us in trouble. They themselves will get into trouble."

Ahmadinejad also seemed to threaten unspecified retaliation, saying his country won't act like it has in the past.

"Definitely, we will show a reaction that will put them to shame," he said.

The IAEA's draft report became public on the same day that Vice President Joe Biden gave a speech in Washington warning about the dangers of nuclear proliferation.

"The spread of nuclear weapons is the greatest threat facing the country -- and I would argue facing humanity -- and that is why we are working both to stop their proliferation and eventually to eliminate them," Biden said in remarks at National Defense University.

CNN's dan Lothian, Charley Keyes and Alan Silverleib contributed to this report