Syria has told the UN atomic watchdog about past nuclear experiments, but is still refusing to cooperate over allegations that it was building a secret nuclear reactor with North Korea's help, a new report revealed Monday.

In a restricted four-page report obtained by AFP, the International Atomic Energy Agency said that Syria "provided the Agency with information concerning previously unreported uranium conversion and irradiation activities" at a small research reactor in Damascus.

Syria insists the scale of the experiment was small, "involving tens of grammes of nuclear material" and took place in 2004.

A senior diplomat familiar with the IAEA investigation said it was too early to determine whether the experiments were purely of a small scientific nature, as Syria claimed, or part of wider, more extensive research.

At the same time, the IAEA complained that Syria had not cooperated with its investigation into allegations that Damascus had been building an undeclared reactor at a remote desert site called Dair Alzour until it was bombed by Israeli planes in September 2007.

The IAEA has been investigating the allegations since 2008 and has already said that the building bore some of the characteristics of a nuclear facility.

UN inspectors also detected "significant" traces of man-made uranium at that site, as yet unexplained by Damascus.

It has also requested access to three other locations allegedly functionally related to Dair Alzour, but so far to no avail.

"As a consequence, the Agency has not been able to make progress towards resolving the outstanding issues related to those sites," the watchdog said.

"Furthermore, with time, some of the necessary information may deteriorate or be lost entirely."

IAEA chief Yukiya Amano urged Syria "to cooperate with the Agency on these issues in a timely manner."

The report is scheduled to be discussed at a meeting of the IAEA's 35-member board of governors at a meeting next week.