The UN nuclear watchdog, the IAEA, is due to meet in Vienna on Thursday.
Iran’s parliament voted on Sunday to end co-operation with UN inspectors and press ahead with uranium enrichment if it is referred to the Security Council.
Diplomats close to the negotiations said Iran would be given more time to consider a compromise that would move the most sensitive part of nuclear fuel production – uranium enrichment – to Russia.
Tehran argues that it has a legitimate right to peaceful nuclear technology.
