[en] The low-lying vibrational states in the even-even deformed nuclei are calculated usually in the harmonic approximation with separable effective forces containing isoscalar components only. In the framework of a model taking into account the quasiparticle-phonon interaction the influence of the anharmonic effects and the isovector components of the multipole-multipole interactions on the structure of vibrational states with Ksup(π)=0⁺, 2⁺, 0^-, 1^-, 2^- in ¹⁵⁴Sm, ¹⁶⁶Er, ²²⁸Th, ²³⁸U, ²⁴⁰Pu is investigated. Energy wave functions (containing one- and two-phonon admixtures) of the first and second excited states and transition probabilities to the ground states are calculated. It is shown that the isovector forces lead to the increase in transition probabilities from the first excited state to the ground one. The calculated energies and transition probabilities are found to be in a good agreement with available experimental data on energies and lifetime of the states under consideration. The calculations testify to the two-phonon nature of the second 0⁺-state in ²⁴⁰Pu