President Barack Obama said Iran's use of nuclear technology "raised grave doubts," as he joined the leaders of Britain and France to demand at the G20 summit in Pittsburgh Friday that Iran open up a secret nuclear facility to United Nations inspectors.

Obama, along with British Prime Minister Gordon Brown and French President Nicholas Sarkozy, chastised Iran for hiding the facility used to manufacture nuclear fuel.

The U.S. president said that Iran needs to "come clean" on its nuclear intentions and hoped that a meeting on October 1 between Iran, the United States and other world powers would lead to resolution of the nuclear standoff.

Obama said that if Iran does not comply, resulting actions could include sanctions and military action.

Also on Friday, the head of Iran's nuclear program suggested UN inspectors will be allowed to visit.

Iran admitted to the existence of the uranium enrichment facility in a letter this week to the UN's International Atomic Energy Agency.

Iran previously claimed to be operating only one plant, which is monitored by the UN.

Iranian President Mahmoud Ahmadinejad maintains that the country is not hiding anything from international inspectors.

Meanwhile, Obama hailed the G20 summit in Pittsburgh a success at regulating the world's economy.

As the two-day summit came to a close, the president said world financial leaders brought the economy back from the brink, saving millions of jobs.

They lined up behind promises to fix the global economic system in hopes of heading off future financial meltdowns.

They also agreed to leave stimulus programs in place for now until recoveries are more firm.

"At the G20, we've achieved a level of tangible, global economic cooperation that we have never seen before, while also acting to address the threat posed by climate change," said Obama. "At the United Nations Security Council, we passed a historic resolution to secure loose nuclear materials to stop the spread of nuclear weapons."

The group of 20 global leaders also agreed to make themselves the lead group for tackling international economic issues in the future, eclipsing the older G8.

Meanwhile, for the second day in a row, protesters took to the streets in Pittsburgh Friday.

The so-called "People's March" took over one of the city's major bridges. Thousands of demonstrators waved flags, banged drums, chanted and sang their opposition to capitalism, human rights violations and the wars in Iraq and Afghanistan.

They also demanded more money for education and job creation.

The protests were not as loud or violent as Thursday's clashes between marchers and police.

Nearly 70 people were arrested.