Context : It is assumed that the unresolved fraction of the X-ray background ( XRB ) consists of a truly diffuse component and a population of the weak sources below the present detection threshold .
Albeit these weak sources are not observed directly , their collective nature could be investigated by statistical means .

Aims : The goal is to estimate the source counts below the conventional detection limit in the Chandra Deep Field-South 2Ms exposure .

Methods : The source number counts are assessed using the nearest neighbor statistics applied to the distribution of photon counts .
The method is described in the first paper of these series .

Results : The source counts down to 3 - 4 \cdot 10 ^ { -18 } cgs in the soft band ( 0.5 - 2 keV ) and down to 2 - 3 \cdot 10 ^ { -17 } cgs in the hard band ( 2 - 8 keV ) are evaluated .
It appears that in the soft band the source counts steepen substantially below \sim 10 ^ { -16 } cgs .
Assuming that the differential slope b \approx 1.5 - 1.6 in the range 10 ^ { -16 } -10 ^ { -14 } cgs , the number of weaker sources indicates the slope of \approx - 2.0 .
The steepening is not observed in the hard band .

Conclusions : Steepening of counts in the soft band indicates a new population of sources .
A class of normal galaxies at moderate redshifts is a natural candidate .