Riot police confront protesters Thursday on Forbes Avenue in Pittsburgh during the G-20 Summit. President Barack Obama and other world leaders opened the summit with a joint statement demanding Iran fully disclose its nuclear ambitions.

PITTSBURGH — Armed with the disclosure of a secret Iranian nuclear facility, President Barack Obama and the leaders of France and Britain demanded today Tehran fully disclose its nuclear ambitions "or be held accountable" to an impatient world community.

French President Nicolas Sarkozy said Iran has until December to comply or face new sanctions. British Prime Minister Gordon Brown accused Iran of "serial deception."

Said Obama: "Iran is breaking rules that all nations must follow."

Their dramatic joint statement opened the G-20 economic summit.

Obama urged the International Atomic Energy Agency to investigate the site.

Iran has kept the facility, 100 miles southwest of Tehran, hidden from weapons inspectors, but the U.S. has long known of its existence, a senior White House official said. Obama decided to go public with the revelation after Iran learned Western intelligence agencies were aware of the project, the official said before the joint statement. The official spoke on grounds of anonymity so as not to pre-empt Obama.

Obama hopes the disclosure will increase pressure on the global community to impose new sanctions on Iran if it refuses to stop its nuclear program. Beyond sanctions, the leaders' options are limited and perilous; military action by the United States or an ally such as Israel could set off a dangerous chain of events in the Islamic world.

In addition, Iran's facilities are spread around the country and well hidden, making an effective military response difficult.

The disclosure comes on the heels of a U.N. General Assembly meeting at which Obama saw a glimmer of success in his push to rally the world against Iranian nuclear ambitions. And it comes days before Iran and six world powers are scheduled to discuss a range of issues including Tehran's nuclear program.

The U.S. has long avoided direct talks with Tehran over its nuclear program.

"The Iranian government must now demonstrate through deeds its peaceful intentions or be held accountable to international standards and international law," Obama said.

In setting the December deadline, Sarkozy said, "Everything, everything must be put on the table now."