The U.S. and its European allies are warning Iran to shut down its nuclear program. With new negotiations scheduled to kick off this week, Iran says "maybe."

But are the Iranians stalling for more time yet again?

As a new round of high-stakes talks begins, the U.S. and its allies plan to give the Islamic Republic a final warning to shut down its nuclear facility deep in an Iranian mountain.

"But time is short. Iran's leaders must understand they too face a choice," President Obama warned. "Iran must act with the seriousness that this moment demands."

Tehran has signaled it might be willing to eventually stop producing its most highly enriched uranium, but it would not totally abandon its ability to make nuclear fuel.

The Israelis want Iran to abandon nuclear enrichment entirely.

"We will continue to follow the talks in order to ensure that Iran doesn't use the talks just to gain time - or even worse - to gain time and deceive the world," Israeli Prime Minister Benjamin Netanyahu said following a meeting with Italian Prime Minister Mario Monti Sunday.

University of Maryland Professor Shibley Telhami said short of a diplomatic deal a confrontation with Iran is inevitable.

"Unless there is a diplomatic deal, nothing is going to stop the opponents of this program from pushing for confrontation with Iran, particularly the Israelis," Tehhami said.

Hundreds of drone and satellite flights over Iran the past three years have provided detailed intelligence of an underground facility, accessed through tunnels.

The intelligence suggests Iran has not taken the step to assemble a bomb -- information the U.S. hopes will stop Israel from launching a preemptive strike.

But the U.S. has made other moves to stop an Israeli strike. Intelligence sources believe the White House may have leaked a secret Israeli plant to use the airfields in Azerbaijan to attack Iran's nuclear facilities. 
 
"I've spoken to one very senior officer who said this is all very damaging, it's all damaging.  If you think about it at the end of the day, there's not strategic surprise anymore," Jerusalem Post military correspondent Yaakov Katz said.