The invention relates to a security strip and security paper for obtaining security documents such as legal tender notes, checks or identification documents, comprising a cellulose support web that is completely embedded in a pulp substrate. As both the substrate and the support web are formed by plant fibers, a series of physical and chemical bonds are established between the fibers of both elements, the support web thus being perfectly integrated in the pulp. The cellulose support web will sometimes have a series of security elements, such as pigments, synthetic elements and/or security fibers of the type normally used in this type of application.