How to break (both) lines at their point(s) of intersection in QGIS?

I'm working with a road network where some of the road segments cross each other but no point is inserted at their intersection. Is there a way to break these line to shorter lines at their points of intersection either completely in QGIS? Thanks

Answer

Try to use GRASS commands via Sextante plugin. Command: v.clean with "break" option.