VIENNA, Austria — The United States and other countries agreed Tuesday to resume negotiations with Iran over its nuclear program.

Iran also signaled a willingness to let international inspectors visit a key military base at Parchin, which international inspectors suspect could be involved in a nuclear weapons program.

The United States, France, Britain, China, Russia and Germany said they would resume stalled talks in a letter from the European Union’s foreign policy chief, Catherine Ashton. She was responding to an overture that Iran made last month.

Israel and the United States suspect Iran is trying to build nuclear weapons. International inspectors also have voiced concern, but Iran insists its nuclear program is for peaceful, civilian purposes.

Israel has spoken openly about the possibility of an attack on Iran’s nuclear program.

President Barack Obama Tuesday cited the possibility of talks at a news conference in Washington, while stressing the “unprecedented pressure” world leaders have been placing on Iran.

“And we’ve got the opportunity, even as we maintain that pressure, to see how it plays out,” he said.

“We’re now seeing noises about them returning to the negotiating table,” Obama said, adding that it “is deeply in everybody’s interests — the United States, Israel and the world’s — to see if this can be resolved in a peaceful fashion.”

When asked whether this was Iran’s final chance for talks — and about remarks Obama made in 2009 saying there would not be talks “forever” — the president did not provide a simple “yes” or “no.” Given “the huge toll” Iran is facing from sanctions and isolation, “they understand that the world community means business,” he said.

Emphasizing the possibility of a diplomatic solution, the president added, “This notion that somehow we have a choice to make in the next week or two weeks or month or two months is not borne out by the facts.”

A top Republican, Senate Minority Leader Mitch McConnell, said Tuesday it “is time to consider a resolution authorizing the use of force,” which would not mandate the use of force but “clearly would indicate to the Iranians that we are willing to go beyond sanctions that many of us are skeptical are likely to get at the final result.” He added that sanctions are useful, however.

At his news conference, Obama said “those who are suggesting or proposing or beating the drums of war should explain clearly to the American people what they think the costs and benefits would be.”

Previous talks with the “P5+1” — the five permanent members of the U.N. Security Council plus Germany — broke off in January 2011 when Iran insisted that all U.N. sanctions be lifted and that the other countries agree that Iran has a right to enrich uranium.

Iran’s offer and the agreement reached Tuesday suggest that Tehran may no longer require such a precondition.

But state-run news agency IRNA said Tuesday that Ali Asghar Khaji, Iran’s deputy foreign minister for Europe and American affairs, “berated the Western governments for ignoring rules of the game in nuclear talks with Iran” and “expressed hope Western governments would adopt a new approach to Iran based on reality, initiative and renovation of past policies.” The report did not make clear what “rules” Khaji was referring to.

While pushing diplomacy, Obama and other U.S. officials emphasize that all options are on the table.

“No greater threat exists to the security of Israel and to the entire region — and indeed the United States — than a nuclear-armed Iran,” U.S. Defense Secretary Leon Panetta said Tuesday in an address to the American Israel Public Affairs Committee, a pro-Israel lobby group.

The United States has made clear that “we want diplomacy to work, we will back the diplomacy with strong and increasing pressure, we will keep all options — including military action — on the table to prevent (Iran) from obtaining a nuclear weapon,” he added.

The top commander of U.S. forces in the Middle East said Tuesday that Iran’s “reckless behavior and bellicose rhetoric have created a high potential for miscalculation.”

Gen. James Mattis, head of the U.S. Central Command, told the Senate Armed Services Committee that threats from Iran “are increasingly maritime” and that the United States will need more assets to respond.

Israeli Prime Minister Benjamin Netanyahu discussed Iran on Monday with Obama in Washington.

“Israel must reserve the right to defend itself, and after all, that’s the very purpose of the Jewish state: to restore to the Jewish people control over our destiny,” he said. He emphasized that Israel will remain “the master of its fate” in ensuring that Iran not obtain a nuclear weapon.

“We’ve waited for sanctions to work,” he said. “None of us can afford to wait much longer. As prime minister of Israel, I will never let my people live in the shadow of annihilation.”

Netanyahu and Obama addressed the AIPAC conference as well.

Obama told the group Sunday that “all elements of American power” remain an option to prevent Iran from developing nuclear weapons.

Iran offered Tuesday to let international nuclear inspectors into its Parchin base, but only after significant details are worked out, its team at the International Atomic Energy Agency said.

The head of the IAEA , the U.N. nuclear watchdog agency, said Monday that inspectors wanted to get into the Parchin site as soon as possible because of evidence of ongoing activities at the military base, which is suspected of being involved in testing related to nuclear weapons.

IAEA Director General Yukiya Amano declined Monday to provide details on whether the activities at that base involve ongoing testing or efforts to remove evidence.

“But I can tell you that we are aware that there are some activities at Parchin and it makes us believe that going there sooner is better than later,” Amano said.

IAEA inspectors had asked to visit the facility during a February trip to Iran but were rebuffed, the agency and Iran have both said.

Iran’s permanent mission to the United Nations agency said Tuesday that the IAEA had been out of line to request access to Parchin, but that once the agency formulated an appropriate request, Iran would let inspectors in.

Iran said Tuesday that the request came “in spite of” an agreement between Iran and the IAEA.

“Considering the fact that it is a military site, granting access is a time-consuming process and cannot be permitted repeatedly,” Iran said.

Nevertheless, it said it would allow access after the IAEA submits paperwork about “all related issues.”

Inspectors believe Iran may have used Parchin to test high explosives that could be used to detonate a nuclear weapon.

IAEA inspectors visited Parchin twice in 2005, but inspectors did not go into the building that housed the test chamber then, according to the IAEA.

Iran offered access to another site late in the February visit, Amano said. But the inspection team in Iran was not outfitted to examine Marivan, a site the IAEA believes may have been used to test elements of a nuclear weapon in 2003.

Iran has said its nuclear program is entirely peaceful, but Amano said Iran’s failure to cooperate with international inspectors makes it impossible to be sure.

In fact, the agency “continues to have serious concerns regarding possible military dimensions” of Iran’s nuclear program, Amano said.

Because Iran is not following an agreement to provide expanded information and broader access to international inspectors, the agency is “unable to provide credible assurance about the absence of undeclared nuclear material and activities in Iran, and therefore to conclude that all nuclear material in Iran is in peaceful activities,” he said in a statement preceding his news conference.

He added that the concern stems from “overall credible information that indicates that Iran engaged in activities relevant to the development of nuclear explosive devices.”

IAEA inspectors traveled to Iran in January and again in February to discuss the issue, but failed to reach an agreement, Amano said.

Monday’s statement by Amano is not the first time the agency has questioned the purposes of Iran’s nuclear program.

Most recently, after the February visit by inspectors, the agency issued a report announcing that Iran had stepped up its efforts to produce enriched uranium in violation of international resolutions calling on it to stop. The agency expressed “serious concerns” about potential military uses by Iran in that report.

Among other things, Iran has tripled its monthly production of uranium enriched to contain a 20 percent concentration of radioactive material and taken other steps to ramp up its nuclear program, Amano said Monday.

While Iran has said the higher-level enrichment is meant to produce therapies for cancer patients and other peaceful purposes, international critics have called the efforts a troubling step toward possible militarization of nuclear technology.

Nuclear weapons require concentrations of about 90 percent.

Amano said the agency would continue discussions with Iran and urged the country to abide by IAEA and U.N. resolutions on its nuclear program.

Iran is under increasing international pressure regarding its nuclear program.

The United Nations, the United States, the European Union and other countries have imposed sanctions related to Iran’s nuclear research, and speculation regarding a possible military strike on Iranian nuclear facilities has been rampant in recent months.

In January, Iran’s state-run Press TV quoted a senior lawmaker saying that in order to hold constructive talks, the West must lift its “illegal sanctions” against Iran.

Press TV reported Tuesday that, “While Tehran says it is ready to continue the talks based on common grounds, it has stressed that it will not give up any of its rights.” The article accused the United States, Israel, and allies of making false accusations against Tehran in order to push for sanctions. “Iran maintains that as a signatory to the nuclear Non-Proliferation Treaty and a member of the International Atomic Energy Agency, it is entitled to develop and acquire nuclear technology for peaceful purposes,” the article said.