A prosecutor in Sweden has opened a preliminary inquiry into a controversial defence deal to help Saudi Arabia build an arms factory, defence officials said Thursday.

Earlier this month public broadcaster Swedish Radio revealed the Swedish Defence Research Agency (FOI) had secret plans since 2007 to help Saudi Arabia build a plant for the production of anti-tank weapons.

Part of the so-called Project Simoom involved, according to Swedish Radio, FOI's alleged creation of a shell company called SSTI to handle dealings with Saudi Arabia, in order to avoid any direct links to FOI and the government.

"There is now a decision from the prosecutor to open a preliminary inquiry," FOI director general Jan-Olof Lind said in a statement, adding that he himself had reported "a suspected crime" to the prosecutor following FOI's own internal review.

"In connection with the internal review some information has been uncovered which has led the authority (FOI) to conclude that a crime may have been committed," FOI said.

It did not specify the nature of the possible crime.

Prosecutor Agneta Hilding Qvarnstroem refused meanwhile to comment.

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 when it broke the story on March 6.

The story has dominated Swedish headlines since then, with numerous politicians and public figures critical of Sweden's plans to provide weapons help to a country they describe as a "dictatorship".

Under pressure to come clean, Defence Minister Sten Tolgfors has admitted he knew of FOI's plans to help Riyadh build the factory and of the shell company.

The opposition Left Party has demanded his resignation, and the opposition Greens Party has reported him to parliament's KU committee which scrutinises ministers' handling of governmental affairs.

Last year, Sweden exported defence material worth a total of 13.9 billion kronor ($2.05 billion, 1.56 billion euros), and Saudi Arabia was the second-biggest buyer, according to the TT news agency.