Evidence suggests Iran has played a key role in supporting war-torn Sudan's weapons production and that Tehran has also been Khartoum's second-biggest supplier of arms, a study said 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".

Khartoum's army spokesman, Sawarmi Khaled Saad, told AFP that many countries, not only Iran, cooperate with Sudan.

There is "nothing peculiar" in Sudan's relations with Iran, Ibrahim Ghandour, the top assistant to President Omar al-Bashir, has said.

"We are not in a military alliance."

China has also reportedly provided training and technical support for Sudanese weapons production, the Small Arms Survey 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.

Two Iranian warships made a call last week in Port Sudan, across the Red Sea from Iran's regional rival Saudi Arabia.

In March, Israel intercepted in the Red Sea a vessel 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 the Gaza Strip, Israel said.

Iran denied any involvement, and Sudan said it had no connection with the vessel which it described as being in international waters.

- Iran a 'significant exporter' -

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.

Jonah Leff, a co-author of the new report, told AFP he did not believe the 2012 "attack" on Yarmouk greatly disabled Khartoum's manufacturing abilities.

"They had already been setting up a new factory by the time it happened," said Leff, who has identified Yarmouk as part of Sudan's Military Industry Corporation (MIC).

"There is scant information available regarding foreign involvement in the MIC's development," the Small Arms Survey report says.

"According to an MIC technician, one of the company's complexes employs 32 Iranian and 37 Sudanese technicians, who operate machinery that was provided by China, although it is overseen by Iranians."

Some highly paid Sudanese technicians are sent to Iran for training, the report said.

Between 2001 and 2012, Iran supplied 13 percent of the small arms and other "conventional weapons" reported as imports by the Sudanese government in a United Nations trade database, Small Arms Survey said.

That was second to China, which supplied 58 percent.

"Iran has been a significant exporter of weapons to Sudan since at least the 1990s," the report said.

"Whereas China's military relationship with Sudan centres on oil and other economic interests, Iran's role in Sudan's defence industry is primarily ideological."

The authorised transfer of "large volumes" of arms to Khartoum since the end of the country's civil war in 2005 does not in itself violate embargoes or agreements, the report said.

But the weapons and ammunition from China, Iran and Sudan "have increasingly found their way to non-state users in Sudan and South Sudan's various conflict arenas."

Sudan itself "has become a significant arms manufacturer in Africa," Small Arms Survey said.

"We manufacture most of our weapons with Sudanese technicians and Sudanese technology," army spokesman Saad said.