UNITED NATIONS: A deal between Iran and key world powers to curb Tehran's nuclear program is working and US President-elect Donald Trump would be wise to preserve it, outgoing US Ambassador to the United Nations Samantha Power said on Friday.

Trump, who will take office in a week, has threatened to either scrap the nuclear agreement or seek a better deal.

"We who see the threat that Iran poses, through its destabilizing actions in the region and through its support for terrorism, would be very wise to preserve an agreement that denies it a weapon of mass destruction," Power told reporters.

"We have succeeded in ensuring that Iran does not develop nuclear weapons ... it's working," she said of the deal Iran made with Britain, France, Germany, China, Russia, the United States and the European Union.

Under the agreement, most UN sanctions were lifted a year ago. But Iran is still subject to an UN arms embargo and other restrictions, which are not technically part of the nuclear agreement.

The United Nations expressed concern to the Security Council that Iran may have violated an arms embargo by supplying weapons and missiles to Lebanese Shi'ite group Hezbollah, according to a confidential report, seen by Reuters on Sunday.

However, the report said that in the past year, the United Nations had not "received any report on the supply, sale, transfer or export to the Islamic Republic of Iran of nuclear-related items undertaken contrary to" a Security Council resolution that enshrines the nuclear deal.

Power said it was important that the Trump administration be "very strong" in enforcing the nuclear deal and "calling out the violations of international norms that occur outside the four corners of the agreement."

"It's important that the communication continue," she said.