(CNN) -- A new International Atomic Energy Agency report on Iran's nuclear activities brings efforts to resolve the crisis to a very "dangerous turning point," an expert on the region said Wednesday.
Another analyst said the United States now faces a choice between only two options: diplomatic engagement or military action. "We have to go one or the other," she said.
Several experts said that there should be new efforts to engage Tehran diplomatically and that additional sanctions are unlikely to get the country to reverse course.
The new report found "credible" information indicating Iran "has carried out activities relevant to the development of a nuclear explosive device," though it found no evidence that the country has decided to actually build a bomb.
Iran insists its nuclear program is solely for peaceful civilian purposes, rejecting complaints from the United States and other countries that it is working toward nuclear weaponry.
On state-run media Wednesday, Judiciary Chief Ayatollah Sadeq Amoli-Larijani was quoted as saying the IAEA report was released under U.S. influence. "You have stockpiles of weapons of mass destruction and that's you who used such bombs against Japan and now introducing yourselves as advocates of human rights," he said, according to IRNA, the Iranian state-run news agency.
But for many other countries, the IAEA report bolsters long-held beliefs that Iran is dishonest about its intentions and suggests that years of international pressure and sanctions have not achieved their goals.
"In the last few weeks, the whole sort of equation has changed," said Geneive Abdo, Iran analyst with The Century Foundation.
"I think we're at a very sort of dangerous turning point right now," she said.
The IAEA report comes weeks after the United States accused elements in the Iranian government of directing a plot to kill Saudi Arabia's ambassador to the United States. U.S. officials said U.S. agents disrupted the plan. Iran denies the accusation.
Pushing another round of sanctions against Iran would not be a good idea, Abdo said. The sanctions so far "have hurt the population," she said, but "the (Iranian) regime doesn't care how much the population suffers."
And sanctions against the Revolutionary Guard Corps and other parts of the Iranian regime have not had many practical effects, she said.
The United States has argued otherwise.
David Cohen, the top Treasury Department official dealing with terrorism and intelligence, told Congress last month, "Our efforts are paying off. Iran is now facing unprecedented levels of financial and commercial isolation."
But Iran's ambassador to the IAEA, Ali Asghar Soltanieh, told CNN on Wednesday, "the sanctions have not had any effect whatsoever on our nuclear activities, including enrichment." He reiterated that there is no nuclear weapons program.
Abdo said she believes Iran won't allow sanctions to affect its nuclear program.
"I think the only move is to have some sort of dialogue with Iran. Whether over Afghanistan or over its nuclear program, the parties have to come back to the negotiating table," she said. "Because the silence is very dangerous. Also, the Iranians, I believe, really believe that there could be an attack now, and they feel completely under siege."
"Historically, the way Iran reacts to pressure is more aggression," and President Mahmoud Ahmadinejad has made clear he reacts that way as well, Abdo said.
Abdo said she does not believe negotiations would lead Iran to halt its alleged efforts to build nuclear weapons. "But I think what's more realistic is they will become more transparent," she said.
"They're not suicidal," she said of the regime, arguing that the government and the population do "not want a military attack."
Shireen Hunter, a professor at Georgetown University's School of Foreign Service, agrees that diplomatic engagement is "worth pursuing."
To do so, the United States would have to avoid actions that contradict those efforts, she said.
"The idea that you can have a dual track -- pressure on the one hand and outreach on the other -- that won't work. It has never worked," Hunter said. "So if we want to pursue engagement, we have to do it really wholeheartedly."
But peaceful efforts might not work, and the other option is not pressure, she said, because "there's nothing much left" to use to pressure the regime. The second option is military action, Hunter said.
"We are really now at a fork. We have to go one or the other."
If the country does decide to take military action, she cautioned, two critical things must be in place: "planning and proper assessments."
Several analysts say that military action is not the way to go.
"Military action is just too risky and has little possibility for payoff," analyst Laicie Olson of The Center for Arms Control and Non-Proliferation said in a blog post for CNN's Global Public Square.
And, she writes, "all peaceful alternatives have not been exhausted."
"More active U.S.-Iranian diplomacy, involving a range of issues about which the two countries differ, would expand the negotiating space, facilitate the reaching of agreements on nuclear matters consistent with U.S. interests, and permit communication to prevent crises from spiraling out of control," she writes.
And some analysts believe there may still be some room for sanctions to make a difference. "The United States almost certainly will and should go to the United Nations, to the United Nations Security Council, and ask for an additional round of sanctions," says Matthew Kroenig of the Council on Foreign Relations.
In a video on the agency's official YouTube site, Kroenig acknowledges that "there's very little left to sanction. But the Iranian central bank is one option, and the United States should push for a round of sanctions against the Iranian central bank."
That said, Russia and China "are almost certain to veto such a proposal," he said. "So it's unclear whether the IAEA report will be a game changer or not."
"Unfortunately, there are very few good policy options for dealing with Iran," Kroenig said.
Soltanieh, the Iranian ambassador to the IAEA, called for negotiations Wednesday. "It is better to stop this childish game," he said in an interview with CNN. "Let's come to the negotiating table, and also let's talk in a civilized manner rather than confrontation."