Police say the offices of Microsoft in Athens have been attacked, with assailants reversing a van through the front entrance and detonating an incendiary device that sparked a fire.

There were no injuries caused in Wednesday's pre-dawn attack on the main offices of Microsoft, north of the city center.

Police said an initial survey of the burned-out van indicated the device consisted of camping gas canisters used to set alight several containers of gasoline.

Initial information indicated three people had been in the van, and they forced two security guards to leave the building before they set it alight.

Police cordoned off the scene, where the van was visible just outside the burned-out entrance of the building.