United States on Monday said reporting Iran to the United Nations Security Council for pressing ahead with its suspect nuclear programme is just a matter of time.
"Clearly our patience is not limited. We're now talking 'when' or 'how' rather than 'whether' we will report them to the Security Council,'' Associated Press said quoting a State Department official who spoke on condition of anonymity.
The UNSC has the power to slap Iran with sanctions.
"Iran is engaged in many activities that raise concern,'' the official said.
"This is all about a weapons program, not a civilian programme. It's a bright red line indicating the Tehran regime is seeking nuclear weaponry," he said.
Envoys from Britain, France and Germany, which have led European efforts to negotiate an end to the standoff, planned to meet in Vienna on December 21 to persuade Tehran to resume talks.
Iran insists its nuclear programme is peaceful and geared solely toward generating electricity, but the United States contends it is covertly trying to make weapons.
On Saturday, Iran's nuclear chief said the country will enrich uranium and produce nuclear fuel domestically despite international efforts to curb its atomic programme.
Enrichment can produce material for use in warheads or fuel for nuclear plants to generate electricity. Tehran already has restarted uranium conversion, a precursor to enrichment.