What is the Iran nuclear deal?
The 2015 nuclear agreement was signed between Iran and five permanent members of the UN Security Council (US, China, Russia, UK and France), plus Germany.
The accord came after years of stand-off between Western nations, which accused Iran of trying to develop nuclear weapons, and Tehran, which said its nuclear programme was for energy only. Sanctions were imposed on Iran over its nuclear programme which badly damaged its economy.
The agreement — aimed at stopping Iran from using its civilian nuclear industry to develop a nuclear weapon in exchange for the lifting of sanctions against Tehran — was signed in July 2015 and implemented in January this year.
What has the US done that is bothering Iran?
US Senate unanimously voted on Thursday to extend the Iran Sanctions Act (ISA) for 10 years. The ISA was first adopted in 1996 to punish investments in Iran's energy industry and deter its alleged pursuit of nuclear weapons.
The decades-old ISA has been repeatedly extended since then and had been due to expire on December 31 this year.
The ISA legislation does not directly address the nuclear pact. But some say the restrictions in the bill go against the spirit of the agreement, under which Tehran curbed its nuclear programme in exchange for sanctions relief from the United States and other nations.
US Lawmakers said the extension would make it easier for sanctions to be reimposed if Iran violated the nuclear settlement.
The bill includes penalties against Iran's banking sector, as well as its energy and defence industries.
How has Iran reacted to it?
Iran says the US Senate's vote to extend the ISA is a violation of the 2015 accord. "The extension of sanctions by the US Congress is a violation of the deal. We will report it to Iran's committee, assigned for monitoring the implementation of the deal," state-run TV quoted Foreign Ministry spokesman Bahram Ghasemi as saying on Friday.
Ghasemi said, "Iran has shown its commitment to its international agreements, but we are also prepared for any possible scenario. We are ready to firmly protect the nation's rights under any circumstances." He did not specify what action Iran would take.
The head of Iran's Atomic Energy Organisation, Ali Akbar Salehi, said the US sanctions legislation "does exist but its effect has been currently neutralised by the US president".
"If it becomes operational again, it's a clear violation," he told state television.
What can we expect next?
President Barack Obama is expected to sign the measure, a White House official said, adding that the administration does not believe the extension violates the nuclear deal.
White House officials said Thursday that Obama remained fully committed to implementing the deal and that the renewal would have no effect at all on the sanctions relief Iran is receiving.
US President-elect Donald Trump heavily criticised the pact as he campaigned for the White House over the past year. Several fellow Republicans have called for its termination. However, several world powers signed onto to the deal and have showed no signs of backing away.