"We should be cautious but cognizant of potentially historic opportunities," Rose Gottemoeller, US assistant secretary of state for arms control told a UN disarmament committee.
"We must continue to push to bring Iran back into line with its international nuclear obligations," Gottemoeller told the forum, which included Iranian diplomats.
"The United States is ready to talk. We are ready to listen. We are ready to work hard and we hope that every country in this room is ready to do the same," Gottemoeller said.
"The road toward the next steps might not be familiar and it will require difficult negotiations and complicated diplomacy," said the US official.
Western nations say they are waiting for the Iranian government to follow up on statements made by President Hassan Rouhani that his country wants an accord to end western doubts about Iran's nuclear drive.
The United States, Britain and France say they believe Iran seeks a nuclear bomb capability. Iran, which is under several rounds of UN sanctions over its uranium enrichment, denies the charge.
Signup to our newsletter and follow us on Facebook and Twitter!
European foreign policy chief Catherine Ashton -- negotiating for the United States, Russia, Britain, France, Germany and China -- is to meet with Iranian negotiators in Geneva next Tuesday.
Western diplomats say this will be a first chance to test Iran's intentions. Rouhani said he wanted a deal within a year. US President Barack Obama has insisted though that Iran must follow up with concrete actions.
Gottemoeller said North Korea, which like Iran faces UN sanctions over its nuclear program, must also "meet its own denuclearization commitments."
"It too can have an opportunity to reintegrate into the international community if it does so," the US official added.
Gottemoeller said there has to be greater international efforts to "further arms reductions, increase transparency, ban the production of fissile material for nuclear weapons use and more."
She renewed calls for the "immediate commencement of long-delayed negotiations on a fissile material cut-off treaty at the (UN) Conference on Disarmament."
"This treaty is the obvious next step in multilateral disarmament and it is time to get to the negotiating table," Goettemoeller said adding to mounting calls made at the meeting for negotiations to start.
Pakistan has repeatedly blocked international attempts to start talks on a treaty to control fissile material for nuclear weapons.