There is described a combined printing press (10; 10*) for the production of security documents, in particular banknotes, comprising a screen printing group (2; 2*) and an intaglio printing group (3) adapted to process substrates in the form of individual sheets or successive portions of a continuous web. The screen printing group (2; 2*) is located upstream of the intaglio printing group (3) and comprises at least one screen printing unit (20; 20*) designed to print a pattern of optically-variable ink onto one side of the substrates, which optically-variable ink contains flakes that can be oriented by means of a magnetic field. The screen printing group (2; 2*) further comprises a magnetic unit (24; 24*) located downstream of the screen printing unit (20; 20*), which magnetic unit is designed to magnetically induce an optically-variable effect in the pattern of optically-variable ink applied by the screen printing unit (20; 20*). The screen printing group (2; 2*) further comprises at least one drying/curing unit (25, 28; 25*, 28*) designed to dry/cure the pattern of optically-variable ink in which the optically-variable effect has been induced by the magnetic unit (24), prior to transfer of the substrates to the intaglio printing group (3).