The UN atomic watchdog carried out an agreed inspection of a Syrian plant on Friday as part of a long-stalled probe into suspected covert nuclear activity.
"The inspection is being conducted as planned," an official of the Vienna-based International Atomic Energy Agency (IAEA) said, giving no further detail.
The visit to the Homs facility in western Syria was part of a wider IAEA inquiry into US intelligence suggesting Syria at another location tried to build a nuclear reactor suited to producing plutonium for atomic bombs.
Syria, which denies any nuclear weapons ambitions, agreed with the IAEA early last month that its inspectors could travel to the Homs acid purification plant, where uranium concentrates, or yellowcake, have been a by-product.
The IAEA saw it as a possible positive step, even though the United States said the gesture would not be enough to address allegations of covert atomic activity.
Letting inspectors only go to Homs would not satisfy Western concerns about Syria, which has stonewalled repeated IAEA requests for further access to a desert site seen as crucial to resolving the matter.
For over two years, Syria has refused IAEA follow-up access to the remains of a complex that was being built at Dair Alzour in the Syrian desert when Israel bombed it to rubble in 2007.
US intelligence reports said it was a nascent North Korean-designed nuclear reactor intended to produce bomb fuel. Inspectors found traces of uranium there in June 2008 that were not in Syria's declared nuclear inventory, heightening concerns.
Syria, an ally of Iran, whose nuclear programme is also under IAEA investigation, denies ever concealing work on nuclear weapons and says the IAEA should focus on Israel instead because of its undeclared nuclear arsenal.
Late last year, after repeated entreaties to Syria's nuclear agency went nowhere, IAEA Director-General Yukiya Amano appealed directly to its foreign minister for cooperation with his agency and access to Dair Alzour and other locations.
As part of its Syria probe, the IAEA has sought to examine the yellowcake at Homs, which if further processed could be used as nuclear fuel. Syria says the plant is for making fertilisers.
Enriched uranium can be used to run nuclear power plants, but also provide material for bombs, if refined much further.
During a 2004 visit to Homs inspectors observed hundreds of kilograms of yellowcake, a confidential IAEA report said.