Evidence suggests Iran has played a key role in supporting war-torn Sudan's weapons production, while Tehran has also been Khartoum's second-biggest supplier of arms, a study said on Monday.
Some of those imported arms, along with others from China, have reached rebel groups in Sudan as well as South Sudan, said the Small Arms Survey report based on more than two years of investigation.
It said that there is "emerging evidence that Iran has played a significant role in supporting Sudan's weapons manufacturing sector".
China has also reportedly provided training and technical support for Sudanese weapons production, the report said.
It cited data showing that most of Sudan's imported small arms, light weapons, ammunition, rocket and grenade launchers have come from China in recent years.
But the report also elaborates on the extent of Sudan's military links with Iran, which have repeatedly been the subject of regional concern and speculation.
"Military ties between Iran and Sudan have grown strong over the years," said the Small Arms Survey, a Swiss-based independent research group.
In March, Israel intercepted in the Red Sea a ship which it said carried M-302 missiles and other weapons shipped from Iran.
They were to have been offloaded at Port Sudan and then taken overland to Palestinian militants in Gaza, Israel said.
Iran denied any involvement, and Sudan said it had no connection with the vessel which it said was in international waters.
In October 2012, Sudan accused Israel of being behind a blast at the Yarmouk military factory in Khartoum, which led to speculation that Iranian weapons were stored or manufactured there.
Israel at that time refused to comment on Sudan's accusation.