The U.S. is not pushing a formal take-it-or-leave-it list of sanctions, but is negotiating with Russia, Great Britain, France and Germany on a package of sanctions it will later present to China, the least enthusiastic member of the Security Council where Iran sanctions are concerned.
The U.S. ambassador to the U.N. gave the first hint of U.S. move Friday.
"We are internally and with partners beginning the process of thinking through what are the appropriate elements of pressure," Susan Rice said. "And that will be a process that will continue over a period of time and I think we should be realistic about the pace."
The U.S. is pushing economic sanctions targeting the Revolutionary Guard Corps, increasingly the dominant military and economic force within the Iranian government.
"They are not like any military as we know it. They're into the repression of the Iranian people and their political aspirations but they are also heavily invested in the Iranian economy," State Department spokesman P.J. Crowley said.
China is not a part of the sanctions talks now because the administration wants to unify the other nations ahead of what promises to be what one official called a "long hard slog."
The strategy is to persuade China to abstain before the Security Council, a move that would allow sanction to proceed without a formal Chinese endorsement.
"As we move toward a U.N. resolution, we think at the end of the day, China will be there and will do its part," Obama said earlier this month.
Movement toward sanctions has intensified recently and is likely to pick up speed following the U.N. nuclear watchdog agency's report that criticized Iran for hiding details about its nuclear program and warned it may be working on a nuclear warhead and missile capability.
"We have no choice. We've spent this past year willing to engage Iran," Crowley said. "We will be taking action in the U.N. in the coming weeks."
Experts say the U.S. must move swiftly to hit Iran.
"Iran has started to enrich its uranium to higher levels," said Sharon Squassoni, director of the proliferation prevention program at the Center for Strategic and International Studies. " So Iran continues to move ahead and we need to move quickly."
"Iran may only be months, or a few years away from a nuclear weapon, so the sooner sanctions are ratcheted up, the better," James Phillips of the Heritage Foundation said.