War-torn Syria has asked the UN atomic watchdog for help in converting a nuclear facility and shipping abroad potentially dangerous nuclear material, the head of the watchdog said Monday.

"We have received a request from Syria early this year... We are studying the request," International Atomic Energy Agency chief Yukiya Amano told reporters.

The assistance would entail converting a small reactor near Damascus so that it can be fuelled with low-enriched uranium (LEU) instead of the more dangerous highly-enriched uranium (HEU).

Syria's stock of around one kilogramme (2.2 pounds) of HEU would then be sent back to China, which built the so-called Miniature Neutron Source (MNSR) reactor that is used for training and research.

HEU can be used inside a nuclear weapon, but this is extremely difficult to do.

A more likely risk in the case of Syria -- where Islamic State militants control swathes of the country -- is that HEU could be used in a so-called "dirty bomb".

This involves dispersing the material over a wide area using conventional explosives, likely causing mass panic.

Governments around the world have made considerable efforts in recent years to convert reactors to use LEU and to reduce HEU stockpiles because of the risks.