"White House expects conversations with Iran on nuclear programme to be difficult and long process"
Some countries believe Iran wants nuclear power because it wants to build a nuclear bomb - it denies this.
In 2015, Iran and six other countries reached a major agreement. Iran would stop some nuclear work in return for an end to harsh penalties, or sanctions, hurting its economy.
Iran re-started banned nuclear work after former US President Donald Trump pulled out of the deal and re-imposed sanctions on Iran. Even though new leader Joe Biden wants to rejoin, both sides say the other must make the first move.
The European Union-brokered Iran nuclear talks, which began in Vienna on Tuesday, is being attended by diplomats from the UK, China, France, Germany, Russia and Tehran.
The US and Iran last week said that they would begin negotiations through intermediaries in a bid to get both the countries back into the landmark 2015 nuclear accord which limits Tehran’s atomic programme. Former president Donald Trump pulled the US out of the deal in 2018.
As the key talks began in Vienna, White House Press Secretary Jen Psaki told reporters at her daily news conference, “We expect this to be -- these conversations to be difficult. We expect this to be a long process. And we're very much at just the beginning period.”