Sweden has in secret been helping Saudi Arabia plan the construction of an arms factory to produce anti-tank missiles, public broadcaster Swedish Radio reported Tuesday.

The Swedish Defence Research Agency (FOI) has helped Saudi Arabia since 2007, though construction on "Project Simoom" has yet to begin, the radio said citing hundreds of classified documents and interviews with key players.

Sweden has in the past sold weapons to Saudi Arabia, but classified government documents state that Project Simoom "pushes the boundaries of what is possible for a Swedish authority," the 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 radio said.

FOI director general Jan-Olof Lind denied the existence of the project.

"We do not have a project agreement with that country," he told the radio.

Asked specifically if there has been a Project Simoom with Saudi Arabia, Lind replied: "No. And I do not wish to comment on discussions that may or may not have occurred between Sweden and Saudi Arabia. These discussions are classified."

But several former FOI employees confirmed the existence of the project to Swedish Radio, including Dick Straeng who led the project until 2010 and was one of Lind's closest colleagues.

"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.

He said the Swedish government was fully aware of the plans.

"Here is a document that the director general signed and sent to the ministry," he said.

The defence ministry refused to comment on the radio's report because of the classified nature of the project.

"I can't comment on the cooperation," state secretary Haakan Jevrell told the radio.

The radio claimed that to avoid any direct links to FOI and the government, FOI set up a company that would handle the dealings with Saudi Arabia.

"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," he added.

Swedish Prime Minister Fredrik Reinfeldt had only a brief comment Tuesday.

"The government is responsible for ensuring that legislation and regulations are in place and followed, and I presume that the responsible authorities have respected the law," he told news agency TT.

The co-head of Sweden's opposition Greens Party demanded Tuesday an investigation, and reported Defence Minister Sten Tolgfors to parliament's KU committee which scrutinizes ministers' handling of governmental affairs.

"KU must examine whether the defence minister's actions are in line with Sweden's democratic ideals and international commitments," Gustav Fridolin said in a statement.

He said a Swedish collaboration with Saudi Arabia would not be beneficial for democracy in the world or Swedish interests.

"Sweden should not ruin its good reputation by supporting the militaries of dictatorships," he said.

In Saudi Arabia, rape, murder, apostasy, armed robbery and drug trafficking are punishable by death, which strictly applies sharia or Islamic law.