Vienna  - Iran has slowed the expansion of its uranium- enrichment programme, but the country still is not cooperating fully with the International Atomic Energy Agency (IAEA), a report by the organization said Thursday.

The report by IAEA head Mohamed ElBaradei stated that since last November only 164 additional centrifuges have started producing low- enriched uranium. Currently, 3,936 such machines are operating, the report said.

Despite three rounds of United Nations Security Council sanctions, Iran has so far rejected calls to suspend its enrichment programme. However, it has offered to guarantee that the programme was only for civil and not for military purposes.

"We see that the pace of installation of centrifuges and of bringing them into operation has slowed considerably in the last months," a senior UN official said Thursday, without speculating on the reason.

Reacting to the report, the United States said that Iran has yet to convince the international community that it has no intention to build nuclear weapons.

Iran's failure to fully cooperate with the IAEA meant "the international community cannot have confidence in the exclusively peaceful nature of Irans programme," State Department spokesman Gordon Duguid said in a statement.

So far, Iran has produced 1,110 kilogrammes of low-enriched uranium. Non-proliferation experts estimate that 1,000 to 1,700 kilogrammes are theoretically needed to enrich the material further for use in an atomic weapon.

Iran has failed to cooperate with the Vienna-based agency in clarifying its past study projects, which could have been connected to nuclear weapons research, ElBaradei wrote in the report obtained by Deutsche Presse-Agentur dpa.

"There remain a number or outstanding issues which give rise to concern," he wrote in the report, which the IAEA governing board is set to discuss in its meeting starting March 2.

The senior UN official said that since August, "Iran has not allowed any discussion" on the issue.

The IAEA has received intelligence from several member states indicating that past research into high explosives, missile design and uranium metal could have been geared toward nuclear weapons work.

Beside asking for more cooperation on these outstanding questions, ElBaradei noted that his inspectors had no access to a heavy-water reactor at Arak, which is still under construction.

To date, the IAEA has monitored activities in the Arak building with the help of satellites. But that is no longer possible, the senior UN official said, as the dome of the building had now been closed.

"The director general continues to urge Iran to implement all measures required to build confidence in the exclusively peaceful nature of its nuclear programme at the earliest possible date," the report said.

The report was released to IAEA member states amid recent signs from the United States and Iran that the two countries might be interested in ending three decades of political estrangement and resume direct talks on Iran's nuclear programmes, along with topics such as the conflicts in Afghanistan and Iraq.

Iranian President Mahmoud Ahmadinejad said Tuesday that his country would not suspend its controversial nuclear-enrichment programme for the sake of improving ties with the United States. (dpa)