A top US official said on Thursday that such a resumption would break an agreement made in February.
"Today ... the government of Iran has informed the United Kingdom, Germany and France that it is resuming production of uranium centrifuge parts," Undersecretary of State for Arms
Control and International Security John Bolton told lawmakers.
Bolton said the US had never believed that Iran had ceased making the parts and the International Atomic Energy Agency (IAEA) board of governors last week said it was troubled that Tehran had continued to do so.
"They have not, at least at this point, said that they would resume actual enrichment activities but it seems to me it is perfectly obvious that Iran is not producing components for uranium centrifuges to use them as knickknacks in Iranian living rooms," Bolton said.
But senior members of the Iranian Parliament accused Britain, France and Germany of breaking promises to facilitate Iran's access to advanced nuclear technology for peaceful purposes.
In a recent Friday sermon, former Iranian president Ayat Allah Ali Akbar Hashemi Rafsanjani alleged there was cooperation between the three European powers and the US to ensure Iran does not attain nuclear technologies for peaceful purposes.
Iran has maintained that its nuclear reactors are for electricity generation and management.
"We never yield to pressure and bullying from anyone," he told the prayer congregation.
Iran had earlier warned it might stop cooperating with the IAEA if Europe passed a resolution condemning Iran's nuclear record.
On 18 June, the IAEA Board of Governors unanimously passed a resolution that sharply rebuked Iran for not cooperating fully with a UN investigation of Tehran's nuclear programme.
It condemned the Islamic Republic's track record saying "Iran's cooperation has not been as full, timely and proactive as it should have been".
'Act of defiance'
The US is rejecting Iranian claims that it is seeking nuclear power for electricity generation and alleges that Iran is pursuing weapons-grade nuclear material.
"This is an act of defiance of the IAEA board of governors. It is a thumb in the eye of the international community," Bolton added.
Enrichment, a process of purifying uranium for nuclear power plants, can also be used to make atomic weapons. If Iran resumed enrichment it would fuel US accusations that Tehran
wants nuclear weapons capability and could provoke a crisis.
The IAEA began investigating Iran after an Iranian exile group reported in August 2002 that Tehran was hiding a massive uranium enrichment facility and other sites from the IAEA.