Tigers in cage

Malicious guards hold tigers in a cage. Set tigers free and hide security guards from them in the same cage.
In a square box 5x5 there are 24 1x1 bars (one place is empty). On four bars the guards are drawn, on the other four bars the tigers are drawn and on sixteen bars pieces of a lattice are drawn.
In the initial position the tigers are in a trap, the guards are outside of a trap (there is an empty place in the centre of a box). Moving bars it is possible to let out the tigers and to hide the guards in the trap.
Three levels (easy, normal and hard) depending on the lattice configuration - the more empty tiles the easier it is to solve this puzzle. It is required to achieve a position in which tigers and security guards interchanged their positions, and the empty place remains in the box center. The target position is visible on a small picture above or to the right of the playing field.