At a press briefing in Washington after Thursday's seven-nation talks concluded in Geneva, the president said inspectors must be given "unfettered access" within two weeks.
Iran must also take steps towards building confidence that the nuclear program is for peaceful purposes only, President Obama said. He warned that patience toward Iran was not unlimited and said that if Iran does not comply with the world powers' demands, the United States is "prepared to move towards increased pressure."
Listen to President Obama's statement:
Iran also agreed in principle Thursday to export much of its stock of enriched uranium for processing, as part of efforts to show the program is not intended to lead to nuclear weapons.
The agreements appeared to mark the most significant progress made in talks with Tehran in more than three years, reported the Guardian.
Earlier in the day, high level U.S. and Iranian delegates met privately during a break in the talks, the first private, high-level talk held between the two countries in years, according to the Washington Post.
U.S. spokesman Robert Wood says U.S. Under Secretary of State William Burns met with Saeed Jalili, Tehran's chief negotiator, but would not elaborate on the content of the meeting.
The United States, Russia, China, Britain, France and Germany were seeking to have Iran freeze its nuclear activities and allow the International Atomic Energy Agency access to the Islamic nation's newly reveled second uranium enrichment plant.
At the talks, Jalili told European Union foreign policy chief Javier Solana that Iran would not give up its "certain rights," state broadcaster IRIB reported, according to Reuters.
Secretary of State Hillary Clinton warned Iran on the eve of the talks that it risks "greater isolation and international pressure" if it does not freeze certain activities and give access to inspectors, reported AFP. The United States is reportedly considering new sanctions if Iran does not comply.
But not all the participating nations have been as eager to go down that road. Both Russia and China have signaled reluctance to impose more sanctions on Iran over its nuclear program in the past.
On the table at the talks is an international offer to suspend sanctions against Iran if it will halt nuclear enrichment. But several parties at the talks have made it clear that patience with Iran over its program will not be indefinite.
"Our message to Iran is simple: Do not mistake respect for weakness," U.K. Foreign Secretary David Miliband told reporters at a press conference.
"You do have the rights to civilian nuclear power, and we are happy for you to exercise them, but not if the price is plunging the Middle East into a nuclear arms race that is a danger to the whole world," he said, according to Bloomberg.
Iranian President Mahmoud Ahmadinejad said Wednesday in Tehran that "the negotiators can adopt any policy they want, but we won't be harmed."
Israel's vice prime minister Silvan Shalom called the talks a "waste of time," saying Iran would never give up its nuclear program, according to the AFP.
---- Compiled from wire reports and other media sources