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

"By the end of the year we should be able to ascertain what Iran's true colors are on this, and the end of the year is coming," Jones said in his first interview with Fox of the Obama presidency. "We're still hopeful. The door is still open, but the window is closing."

Asked what would happen if by year's end the Iranians had not agreed to their own proposal to move lightly-enriched uranium to Russia and France for reprocessing, Jones said sanctions would appear to be an inevitable consequence.

"I think you have to go on to the next step, and we have been in consultation with a large number of countries, there's a general cohesion on this issue that this is an important milestone that won't be taken lightly," Jones said.

Asked specifically if there were any options under consideration that did not involve sanctions against Iran, Jones said:

"Not on the table at this point other than endless negotiations which the president has said he will not engage in," Jones said. "Six, seven months is enough time for them to do this. So we hope, and we're still hopeful, but they certainly haven't given us reason to think that it's going to change."

Iran has refused to embrace an agreement its own representatives negotiated on Oct. 1 with U.N.-backed nuclear watchdogs to reprocess about 2,600 pounds of lightly enriched uranium, which constitutes nearly 70 percent of its known supplies - in Russia and repackaged in France so it can be used in a research reactor in Tehran for production of medical isotopes. Obama has said if Iran turns this agreement into action it could boost confidence that Iran's nuclear energy program is, as the regime has often said, strictly related to civilian energy needs.

As other top Obama advisers have said, Jones underlined the choice ahead for the Iranian regime.

"We've been working with the existing organizations, the IAEA (International Atomic Energy Agency), all friends and allies to counsel patience and to give the Iranians time to decide how they want to show themselves to the world," Jones said. "Do they want to have a more constructive, peaceful relationship or is it going to be the path of competition and confrontation?"

Russian President Dmitri Medvedev has expressed his frustration with Iranian foot-dragging on the reprocessing issue and pointedly endorsed the concept of as-yet-undefined U.N.-approved sanctions. Chinese President Hu Jintao has declined to publicly pressure Iran, a supplier of roughly 15 percent of China's annual oil consumption. But White House officials say private talks have led them to conclude China will not block sanctions if the need arises.