US Secretary of State Hillary Clinton said Friday there would be "increasing activity" in the near future towards a package of UN sanctions on Iran over its disputed nuclear program.

Clinton said the Obama administration had held "constructive talks" with all its partners and in-depth consultations with Russia and other international partners on sanctions.

"We are working on language," Clinton said, after President Barack Obama agreed a new nuclear arms treaty with Russia.

"I believe that you will see increasing activity in the very near future as we work to bring to fruition a resolution that can muster the votes that are necessary in the Security Council."

The United States, Russia, China, Britain and France -- the five veto-wielding permanent UN Security Council members -- plus Germany have led efforts to curb Iran's uranium enrichment program.

However, China is most opposed to a tougher set of sanctions than the three previous rounds.

On Thursday, the Wall Street Journal reported that Washington had agreed to soften proposed measures against Iran to win the backing of China and Russia, which had also been seen as less keen to embrace biting sanctions.

The newspaper said proposals that would have effectively closed international airspace and waters to Iranian state-owned air cargo and shipping lines had been scrapped.

The report had "significant inaccuracies," Clinton's spokesman Philip Crowley told reporters.

"Since we have not circulated a draft resolution, it's hard to say at this point that we're watering anything down. There's nothing to water down. There's nothing to take off the table," he said.

The parties were simply "trading ideas" at this point on how to draft an appropriate resolution that shows "our shared concern" about Iran's actions, he added.