Sweden has been helping Saudi Arabia construct an anti-tank missile factory in secret for the past four years, a radio station has claimed.

Public broadcaster Swedish Radio said the country's Defence Research Agency (FOI) began helping the Saudi's plan the construction of the plant in secret in 2007, but added that construction had not started on Project Simoom.

Sweden has previously sold weapons to Saudi Arabia, but the latest revelations push the boundaries of what is possible for a Swedish authority, the report said, according to the Associated Press.

Citing hundreds of classified documents and interviews with former employees, Swedish Radio said The fact that an authority such as FOI is involved in the planning of a weapons factory for a government in a dictatorship such as Saudi Arabia is quite unique.

The station spoke to Dick Straeng, former project leader of Simoom until 2010, who said the Swedish government was fully aware of the plans.

If I were to contradict your claims I would have to say that the documents you are showing me are fakes, and they are not, he said when presented with the classified material.

According to Swedish Radio, the FOI set up a separate company, SSTI, to deal with construction on Simoom.

The report claimed SSTI was meant to keep the Swedish government at arm's length from any dealings with the Saudi authorities and to get around export restrictions faced by the FOI.

Under Swedish law all military exports are subject to regulation by the Swedish Agency for Non-Proliferation and Export Controls.

FOI has, as far as the defence ministry knows, no collaboration with the company mentioned in the radio report, Defence Minister Sten Tolgfors wrote on his blog.

There are no government decisions giving FOI a mandate to build a factory for weapons production, the AP reported him writing.