Iran's supreme leader has dismissed a US offer of one-to-one talks on Tehran's nuclear programme.
Ayatollah Ali Khamenei said in a speech posted online that the US was proposing talks while "pointing a gun at Iran".
On Saturday, US Vice-President Joe Biden suggested direct talks, separate to the wider international discussions due to take place later this month.
But the US widened sanctions on Iran on Wednesday, aiming to tighten a squeeze on Tehran's ability to spend oil cash.
Iran, which is subject to an array of international sanctions, has long argued that its nuclear programme is for energy generation and research.
Tehran's critics believe the government is developing nuclear weapons.
The five permanent members of the UN Security Council plus Germany have held a series of negotiations with Iran over the years.
But they have often ended with Iran demanding the West lifts sanctions as a condition to any nuclear move, and the Western powers refusing.
Iran is expected to attend another round of negotiations on 26 February in Kazakhstan.