Hossein Entezami, spokesman for the Supreme National Security Council, told Reuters on Saturday: "Inspectors from the International Atomic Energy Agency, (IAEA), arrived in Tehran last night.
"The research will be started in co-ordination with the agency."
Iran's decision to resume atomic fuel research has drawn fire from the United States and Europe, which suspect Tehran to be secretly working on nuclear arms. Tehran denies this.
European diplomats speculate that resuming research on nuclear fuel could amplify calls for Iran to be sent to the UN Security Council for possible sanctions.
It is not exactly clear what Iran's nuclear fuel research will entail - whether it will just be tests on equipment or actually involve small amounts of uranium being enriched in a laboratory environment.
Washington has said a resumption of nuclear fuel research would signal that Tehran was not interested in a diplomatic solution to the nuclear dispute.
Much of the international community has called on Iran to give up its work on nuclear fuel and send its uranium to Russia to be enriched there.
Iran insists the fuel needed for its nuclear power station at the southern port of Bushehr must be produced domestically.