We report on the observation of additional sub-Doppler lines in a saturated absorption experiment when exploring the vicinity of the $6{S}_{1/2}\ensuremath{-}8{P}_{3/2}$ transition of Cs (\ensuremath{\lambda}$=$388 nm). These additional lines are observed only under a relatively strong irradiation of both the pump and the probe beams. Extra narrow lines are also observed in copropagating nonlinear spectroscopy, and around the lines of the V-type three-level system $8{P}_{3/2}\ensuremath{-}6{S}_{1/2}\ensuremath{-}8{P}_{1/2}$ (${\ensuremath{\lambda}}_{1}$$=$388 nm, ${\ensuremath{\lambda}}_{2}$$=$389 nm). We attribute theses additional lines to a probing of high-lying molecular cesium, produced as a result of the optical excitation of Cs atoms, as the low Cs atom density (\ensuremath{\le}10${}^{12}$cm${}^{\ensuremath{-}3}$) is unable to populate significantly the dimer states in the condition of thermal equilibrium.