A senior State Department official, speaking on the condition of anonymity, added later: "There's nothing really new in the package itself."
In an interview with the Washington Post, President Mahmoud Ahmadinejad's senior adviser Mojtaba Samareh Hashemi said the package calls for setting up an international system to scrap and prevent nuclear weapons worldwide.
But Hashemi did not reply directly when asked if it contained a promise to meet international demands to halt uranium enrichment.
He suggested Iran aims to establish an international system in which nobody will be allowed to make nuclear weapons -- rather than to build an atomic weapon itself.
"Iran not only does not want to make nuclear weapons, but is actually intensely against nuclear weapons," Hashemi told the newspaper. "In all truth, Iran is trying to establish a new regime to prevent nuclear weapons worldwide."
Iran has long called for Israel to scrap its widely suspected stockpile of nuclear weapons.
He added that the package also calls for a broad range of cooperation in promoting regional and international security as well as fighting drugs smuggling, terrorism and organized crime.
These efforts, he told the newspaper, would include help in neighboring Afghanistan, something President Barack Obama's administration has sought.
Crowley said the United States would consult again Friday with its partners in the so-called P5-plus-1 -- or the permanent five veto-wielding members of the UN Security Council, plus Germany -- after consulting them Wednesday.
"We'll be looking to see how... ready Iran is to actually engage. And we will be testing that willingness to engage in the next few weeks," Crowley said.
The world powers -- meeting on Iran for the last three years -- have given Tehran a late September deadline to begin negotiations with them about the atomic program or face more sanctions. Tehran is already under three sets of UN sanctions.
Taking a more conciliatory approach toward Tehran than his predecessor George W. Bush, Obama has been reaching out to the Iranian leadership to begin talks on its nuclear program and other issues.
Washington and Tehran have had no diplomatic relations since a year after the 1979 Islamic revolution in Iran which toppled the US-backed shah.
China meanwhile called on all parties to step up efforts to resolve the standoff.
"We believe that under the current circumstances, relevant parties should step up diplomatic efforts and resume talks as soon as possible to seek a comprehensive, long-term and proper settlement of the issue," Chinese foreign ministry spokeswoman Jiang Yu told journalists in Beijing.
Russia, too, said it was evaluating the latest Iranian proposals.
Foreign Minister Sergei Lavrov said Iran's new proposals offered material to work with and called on world powers to issue a unified response.
"There is something to dig into," Lavrov said.
He repeated Russia's resistance to the use of sanctions.
Britain, whose relations with Iran have deteriorated since the disputed re-election of Ahmadinejad on June 12, said it was "committed to a meaningful dialogue" to address concerns over Tehran's atomic drive.
Iran has accused Britain of having a role in the post-election unrest in Tehran which officials say killed about 36 people.
According to the Iranian media, Iran's envoy to the International Atomic Energy Agency (IAEA) again insisted at the agency's meeting in Vienna that Tehran will continue enriching uranium.
On Wednesday, the US envoy to the IAEA, Glyn Davies, said Iran may have enough nuclear material already to put together an atomic bomb.
But IAEA chief Mohamed ElBaradei, who last week alleged the Iranian threat had been "hyped", said there was no need to panic.
Washington fears the nuclear program will be used to build an atom bomb. Iran denies the charge, saying it is aimed at generating electricity.