The move by the new Biden administration comes ahead of a planned EU-led meeting to discuss a return to the Iran nuclear deal
The United States has indicated it is ready to return to talks on the Iran nuclear deal after reversing a move by former president Donald Trump to reimpose all sanctions.
In an announcement late on Thursday night the State Department also said it was easing travel restrictions on Iranian diplomats posted to the United Nations in New York.
The moves came ahead of meetings of the G7 group of industrialised countries and the annual Munich Security Conference on Friday.
President Joe Biden is expected to speak at both.
Iran's foreign minister Javad Zarif said his country would "immediately reverse" its countermeasures if the US lifted sanctions.
The US had declared last September that all United Nations sanctions were restored because of Iran’s “significant non-performance” of its obligations under the 2015 deal, known as the Joint Comprehensive Plan of Action (JCPOA).
The legality of that declaration was questioned at the time by Britain, France and Germany.
In response, Iran began uranium enrichment beyond the levels agreed in the JCPOA.
But in a letter to the UN Security Council on Thursday, the acting US ambassador Richard Mills said his country “hereby withdraws” the three letters sent by the Trump administration.
The US also said it would accept an invitation from the EU's foreign policy chief Josep Borrell to discuss the Iran nuclear deal at a meeting of its participants.
Iran analyst Soraya Lennie said there was a "lot of damage [to the original deal] that needs to be undone".
Speaking to Euronews's Good Morning Europe programme, she said: "Keep in mind that Iran did adhere to this deal for a really long time, including after the election of Donald Trump, including after the United States withdrew from the deal and started to reimpose damaging economic sanctions.
"It's only very recently, probably within the last 18 months, that Iran really did try to escalate and renege from some of its commitments.
"But it was always very consistent in the message that whatever it was doing is easily reversible and that's still the Iranian position".
In Iran, state television quoted President Hassan Rouhani earlier on Thursday as expressing hope that the Biden administration will rejoin the accord and lift the US sanctions that Washington re-imposed under Trump.
The 2015 deal was signed by the five permanent members of the UN Security Council and Germany, known as the P5+1, along with Iran.
State Department spokesman Ned Price said on Thursday: “The United States would accept an invitation from the European Union High Representative to attend a meeting of the P5+1 and Iran to discuss a diplomatic way forward on Iran’s nuclear programme.”