International sanctions are slowing Iran's nuclear program but the Islamic Republic has repeatedly sought to breach an arms embargo by shipping weapons to Syria, UN investigators said in a report.

Six of the nine violations of a UN ban on conventional arms shipments by Iran involve Syria, said the report, a copy of which was obtained by AFP.

The UN Security Council has passed four rounds of sanctions against Iran over its uranium enrichment, which western nations say is a front for a nuclear arms drive. A panel of experts which monitors the sanctions said Iran is circumventing the action but that nuclear work has been hit.

The sanctions are "slowing Iran's nuclear program but are not yet having an impact on the decision calculus of its leadership with respect to halting uranium enrichment and heavy water-related activities."

Iran is believed "to be coming close to exhausting its supply of uranium oxide." It may therefore be seeking new sources of uranium to expand its enrichment.

The international embargoes, assets freezes and travel bans have "clearly forced changes in the way in which Iran procures items," said the report.

"At the same time, Iran's circumvention of sanctions across all areas, in particular front companies, concealment methods in shipping, financial transactions, and the transfer of conventional arms and related materiel, is willful and continuing."

The panel of experts recommended adding the names of new individuals and companies to the UN sanction list.

Iran, which insists its nuclear work is peaceful, has sought "to procure equipment and technology that fall below the thresholds for listed items, but which are still useful, in an attempt to evade sanctions."

The report said Iran has tried to purchase nuclear technology subject to export controls by placing orders with intermediaries in countries without rigorous export oversight. The front companies, set up by Iran's Revolutionary Guard and other entities, send the technology on to Iran.

"The panel notes that most reported incidents of conventional arms-related violations involve Syria, which has a long and close relationship with Iran," said the report.

"In all such incidents inspected by the panel, prohibited material was carefully concealed to avoid routine inspection and hide the identity of end-users."

The experts said it was likely that other undetected arms shipments had been made and that "other illicit shipments were identified but not reported" to the UN sanctions committee.

Israel seized on Iranian shipment to the Hamas group in Gaza, which was carried out through Syria. Nigeria also seized an Iranian arms shipment last year and is prosecuting an Iranian allegedly involved.

The panel said Turkey, Cyprus, Britain and Germany had also reported arms violations.