The United States and its allies are stepping up their rhetoric against Iran, warning that they will impose "significant" international sanctions, possibly in a matter of weeks, if the country continues with its nuclear program. 

The warnings suggest a turning point in the global community's attitude toward Iran. Western nations for months have made vague threats against the Islamic nation while working toward a compromise. But with Iran persistently defying international pressure, the bluster could turn into penalties. 

Defense Secretary Robert Gates said Friday that sanctions are coming "soon" if Iran continues its current program, and he reiterated that all options, including military action, must stay on the table. The Obama administration is looking to press for new United Nations sanctions in early January. 

"I think that you are going to see some significant additional sanctions imposed by the international community," Gates said, adding that "any military action would only buy some time, maybe two or three years." 

Gates' comments came a day after United States, Britain and France warned that Iran risks increased sanctions unless it immediately complies with a series of Security Council resolutions regarding its nuclear program. 

Mark Grant, Britain's U.N. ambassador, reportedly said discussions would start "at the beginning of the year" over sanctions. France's ambassador, Gerard Araud, echoed that threat. 

The United States and its allies believe Iran is using its nuclear program as a cover for building a bomb. Tehran says it only wants to build nuclear reactors to generate electricity. 

But John Bolton, former U.S. ambassador to the United Nations during the Bush administration, said he doubts Iran's momentum toward a nuclear weapon can be halted, even if there's a new round of sanctions. 

"New sanctions, however strong, are not going to dissuade them from pursuing that capability," he told Fox News. "So there are a lot of questions that remain here."

Obama's year-end deadline for Iran is fast-approaching, and the United States is trying to reach out to Russia and China as well as European allies to win support for new penalties. 

During a meeting last month with Russian President Dmitry Medvedev, Obama said "we are now running out of time" for Iran to sign on to a deal to ship its enriched uranium out of the country for further processing. 

National Security Adviser James Jones also told Fox News in early December that "the window is closing" for Iran to reverse course on its nuclear program and that the White House will push for tough new sanctions if no progress is achieved by year's end. 

During his Nobel Peace Prize acceptance speech in Oslo on Thursday, Obama made a stern reference to Iran's defiance. 

"Those who claim to respect international law cannot avert their eyes when those laws are flouted," Obama said. "Those who care for their own security cannot ignore the danger of an arms race in the Middle East or East Asia. Those who seek peace cannot stand idly by as nations arm themselves for nuclear war." 

Fox News' Major Garrett and The Associated Press contributed to this report.