"I think they should understand that because the international community has applied so many sanctions, because we have employed so many of the options that are available to us to persuade Iran to take a different course," Obama said, "that the window for solving this issue diplomatically is shrinking."

Iran has shown a tendency in the past to "delay, to stall, to do a lot of talking," Obama said, but has not taken steps to dismantle its nuclear program.

In a joint news conference in the White House Rose Garden, Obama and British Prime Minister David Cameron appeared to ratchet up the pressure on Iran to engage in serious negotiations.

REPORTING FROM WASHINGTON -- President Obama warned Iran on Wednesday that the window of opportunity to resolve the international deadlock over its nuclear weapons program through diplomacy is closing.

The United States and many of its allies suspect that Iran's nuclear program is geared toward developing weapons, though the Tehran regime insists that its goals are peaceful.

The sharpening of Obama's language was slight but significant since Tehran has offered to resume negotiations with the U.S. and five other world powers. Iranian officials nevertheless have refused to allow International Atomic Energy Agency inspectors to enter its Parchin military base, as the United Nations inspectors have requested for several months, to search for possible evidence of nuclear development.

U.S. officials said Wednesday that the president wasn't responding to a particular development, but was taking note of the Iranians' past practice of holding out the possibility of negotiations in order to stall for time.

Obama did not make an explicit threat, but the possibility of a military strike against Iranian nuclear facilities was clear. Cameron issued an oblique reminder of it.

"We are serious about the talks that are set to resume, but the regime has to meet its international obligations," he said. "As the president and I have said, nothing is off the table. That is essential for the safety of the region and the wider world."

Earlier this month, Obama met with Israeli Prime Minister Benjamin Netanyahu and other Israeli officials and urged them to hold off on a possible military attack on Iran to give time for diplomacy to work. The president also argued that Iran will increasingly feel the bite of unprecedented economic sanctions in coming months.

On Wednesday, though, Obama suggested that the offer to negotiate won't last forever.

"We will do everything we can to resolve this diplomatically," Obama said. "But ultimately we've got to have somebody on the other side of the table who's taking this seriously, and I hope that the Iranian regime understands that, that this is their best bet for resolving this in a way that allows Iran to rejoin the community of nations and to prosper and feel secure themselves."

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-- Christi Parsons and Paul Richter

Photo: With British Prime Minister David Cameron at his side, President Obama addresses a news conference in the White House Rose Garden on Wednesday. Credit: Joshua Roberts / Bloomberg

