Moscow has already voiced opposition to prolonging the ban on conventional arms sales to Tehran, with Russian firms expecting to conclude major deals if restrictions end.

Kelly Craft, the US ambassador to the United Nations, said Washington had shared a draft resolution on the extension with Russia as well as Western allies Britain, France, Germany and Estonia which are all on the 15-nation Security Council.

"Pretty soon we'll be sharing (with) the full 15. But, you know, we are trying to really work very carefully, very thoroughly," Craft told reporters.

"Russia and China need to join a global consensus on Iran's conduct," she said.

"This is an absolute imperative that we exercise all of our options to make certain that this UN arms embargo is extended."

The arms embargo's expiration date is part of a 2015 UN Security Council resolution that blessed a multinational deal on ending Iran's nuclear program.

The five-year window was a compromise between President Barack Obama's administration and Russia and China, which wanted an immediate end.

President Donald Trump in 2018 withdrew from the accord, calling it the "worst deal ever."

But his administration has made the novel argument that the United States remains a participant in the deal under the resolution and can trigger UN sanctions for Iran's non-compliance with the 2015 deal -- an option it could take if others do not back the arms embargo.

Iran, which has taken steps away from the 2015 deal in response to unilateral US sanctions imposed by Trump, has warned that the extension of the embargo would mean the death of the nuclear accord.